![[Experimental]](https://dbi.r-dbi.org/reference/figures/lifecycle-experimental.svg)
DBI defines an interface for communication between R and relational database management systems. All classes in this package are virtual and need to be extended by the various R/DBMS implementations (so-called DBI backends).
A DBI backend is an R package which imports the DBI and methods packages. For better or worse, the names of many existing backends start with ‘R’, e.g., RSQLite, RMySQL, RSQLServer; it is up to the backend author to adopt this convention or not.
A backend defines three classes,
which are subclasses of
DBIDriver,
DBIConnection,
and DBIResult.
The backend provides implementation for all methods
of these base classes
that are defined but not implemented by DBI.
All methods defined in DBI are reexported (so that the package can
be used without having to attach DBI),
and have an ellipsis ... in their formals for extensibility.
The backend must support creation of an instance of its DBIDriver subclass
with a constructor function.
By default, its name is the package name without the leading ‘R’
(if it exists), e.g., SQLite for the RSQLite package.
However, backend authors may choose a different name.
The constructor must be exported, and
it must be a function
that is callable without arguments.
DBI recommends to define a constructor with an empty argument list.
RSQLite::SQLite()
This section describes the behavior of the following method:
dbDataType(dbObj, obj, ...)
Returns an SQL string that describes the SQL data type to be used for an object. The default implementation of this generic determines the SQL type of an R object according to the SQL 92 specification, which may serve as a starting point for driver implementations. DBI also provides an implementation for data.frame which will return a character vector giving the type for each column in the dataframe.
dbObj |
A object inheriting from DBIDriver or DBIConnection |
obj |
An R object whose SQL type we want to determine. |
... |
Other arguments passed on to methods. |
The data types supported by databases are different than the data types in R, but the mapping between the primitive types is straightforward:
Any of the many fixed and varying length character types are mapped to character vectors
Fixed-precision (non-IEEE) numbers are mapped into either numeric or integer vectors.
Notice that many DBMS do not follow IEEE arithmetic, so there are potential problems with under/overflows and loss of precision.
dbDataType() returns the SQL type that corresponds to the obj argument
as a non-empty
character string.
For data frames, a character vector with one element per column
is returned.
An error is raised for invalid values for the obj argument such as a
NULL value.
The backend can override the dbDataType() generic
for its driver class.
This generic expects an arbitrary object as second argument.
To query the values returned by the default implementation,
run example(dbDataType, package = "DBI").
If the backend needs to override this generic,
it must accept all basic R data types as its second argument, namely
logical,
integer,
numeric,
character,
dates (see Dates),
date-time (see DateTimeClasses),
and difftime.
If the database supports blobs,
this method also must accept lists of raw vectors,
and blob::blob objects.
As-is objects (i.e., wrapped by I()) must be
supported and return the same results as their unwrapped counterparts.
The SQL data type for factor and
ordered is the same as for character.
The behavior for other object types is not specified.
All data types returned by dbDataType() are usable in an SQL statement
of the form
"CREATE TABLE test (a ...)".
dbDataType(ANSI(), 1:5)
dbDataType(ANSI(), 1)
dbDataType(ANSI(), TRUE)
dbDataType(ANSI(), Sys.Date())
dbDataType(ANSI(), Sys.time())
dbDataType(ANSI(), Sys.time() - as.POSIXct(Sys.Date()))
dbDataType(ANSI(), c("x", "abc"))
dbDataType(ANSI(), list(raw(10), raw(20)))
dbDataType(ANSI(), I(3))
dbDataType(ANSI(), iris)
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbDataType(con, 1:5)
dbDataType(con, 1)
dbDataType(con, TRUE)
dbDataType(con, Sys.Date())
dbDataType(con, Sys.time())
dbDataType(con, Sys.time() - as.POSIXct(Sys.Date()))
dbDataType(con, c("x", "abc"))
dbDataType(con, list(raw(10), raw(20)))
dbDataType(con, I(3))
dbDataType(con, iris)
dbDisconnect(con)
This section describes the behavior of the following method:
dbConnect(drv, ...)
Connect to a DBMS going through the appropriate authentication procedure.
Some implementations may allow you to have multiple connections open, so you
may invoke this function repeatedly assigning its output to different
objects.
The authentication mechanism is left unspecified, so check the
documentation of individual drivers for details.
Use dbCanConnect() to check if a connection can be established.
drv |
an object that inherits from DBIDriver, or an existing DBIConnection object (in order to clone an existing connection). |
... |
authentication arguments needed by the DBMS instance; these
typically include |
dbConnect() returns an S4 object that inherits from DBIConnection.
This object is used to communicate with the database engine.
A format() method is defined for the connection object.
It returns a string that consists of a single line of text.
DBI recommends using the following argument names for authentication
parameters, with NULL default:
user for the user name (default: current user)
password for the password
host for the host name (default: local connection)
port for the port number (default: local connection)
dbname for the name of the database on the host, or the database file
name
The defaults should provide reasonable behavior, in particular a
local connection for host = NULL. For some DBMS (e.g., PostgreSQL),
this is different to a TCP/IP connection to localhost.
In addition, DBI supports the bigint argument that governs how
64-bit integer data is returned. The following values are supported:
"integer": always return as integer, silently overflow
"numeric": always return as numeric, silently round
"character": always return the decimal representation as character
"integer64": return as a data type that can be coerced using
as.integer() (with warning on overflow), as.numeric()
and as.character()
# SQLite only needs a path to the database. (Here, ":memory:" is a special
# path that creates an in-memory database.) Other database drivers
# will require more details (like user, password, host, port, etc.)
con <- dbConnect(RSQLite::SQLite(), ":memory:")
con
dbListTables(con)
dbDisconnect(con)
# Bad, for subtle reasons:
# This code fails when RSQLite isn't loaded yet,
# because dbConnect() doesn't know yet about RSQLite.
dbListTables(con <- dbConnect(RSQLite::SQLite(), ":memory:"))
This section describes the behavior of the following method:
dbDisconnect(conn, ...)
This closes the connection, discards all pending work, and frees resources (e.g., memory, sockets).
conn |
A DBIConnection object, as returned by
|
... |
Other parameters passed on to methods. |
dbDisconnect() returns TRUE, invisibly.
A warning is issued on garbage collection when a connection has been
released without calling dbDisconnect(),
but this cannot be tested automatically.
A warning is issued immediately when calling dbDisconnect() on an
already disconnected
or invalid connection.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbDisconnect(con)
This section describes the behavior of the following method:
dbSendQuery(conn, statement, ...)
The dbSendQuery() method only submits and synchronously executes the
SQL query to the database engine. It does not extract any
records — for that you need to use the dbFetch() method, and
then you must call dbClearResult() when you finish fetching the
records you need.
For interactive use, you should almost always prefer dbGetQuery().
Use dbSendQueryArrow() or dbGetQueryArrow() instead to retrieve the results
as an Arrow object.
conn |
A DBIConnection object, as returned by
|
statement |
a character string containing SQL. |
... |
Other parameters passed on to methods. |
The following arguments are not part of the dbSendQuery() generic
(to improve compatibility across backends)
but are part of the DBI specification:
params (default: NULL)
immediate (default: NULL)
They must be provided as named arguments. See the "Specification" sections for details on their usage.
No warnings occur under normal conditions.
When done, the DBIResult object must be cleared with a call to
dbClearResult().
Failure to clear the result set leads to a warning
when the connection is closed.
If the backend supports only one open result set per connection,
issuing a second query invalidates an already open result set
and raises a warning.
The newly opened result set is valid
and must be cleared with dbClearResult().
The param argument allows passing query parameters, see dbBind() for details.
immediate argumentThe immediate argument supports distinguishing between "direct"
and "prepared" APIs offered by many database drivers.
Passing immediate = TRUE leads to immediate execution of the
query or statement, via the "direct" API (if supported by the driver).
The default NULL means that the backend should choose whatever API
makes the most sense for the database, and (if relevant) tries the
other API if the first attempt fails. A successful second attempt
should result in a message that suggests passing the correct
immediate argument.
Examples for possible behaviors:
DBI backend defaults to immediate = TRUE internally
A query without parameters is passed: query is executed
A query with parameters is passed:
params not given: rejected immediately by the database
because of a syntax error in the query, the backend tries
immediate = FALSE (and gives a message)
params given: query is executed using immediate = FALSE
DBI backend defaults to immediate = FALSE internally
A query without parameters is passed:
simple query: query is executed
"special" query (such as setting a config options): fails,
the backend tries immediate = TRUE (and gives a message)
A query with parameters is passed:
params not given: waiting for parameters via dbBind()
params given: query is executed
This method is for SELECT queries only. Some backends may
support data manipulation queries through this method for compatibility
reasons. However, callers are strongly encouraged to use
dbSendStatement() for data manipulation statements.
The query is submitted to the database server and the DBMS executes it,
possibly generating vast amounts of data. Where these data live
is driver-specific: some drivers may choose to leave the output on the server
and transfer them piecemeal to R, others may transfer all the data to the
client – but not necessarily to the memory that R manages. See individual
drivers' dbSendQuery() documentation for details.
dbSendQuery() returns
an S4 object that inherits from DBIResult.
The result set can be used with dbFetch() to extract records.
Once you have finished using a result, make sure to clear it
with dbClearResult().
This section gives a complete overview over the flow for the execution of queries that return tabular data as data frames.
Most of this flow, except repeated calling of dbBind() or dbBindArrow(),
is implemented by dbGetQuery(), which should be sufficient
unless you want to access the results in a paged way
or you have a parameterized query that you want to reuse.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendQuery() to create a result set object of class
DBIResult.
Optionally, bind query parameters with dbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbColumnInfo() to retrieve the structure of the result set
without retrieving actual data.
Use dbFetch() to get the entire result set, a page of results,
or the remaining rows.
Fetching zero rows is also possible to retrieeve the structure of the result set
as a data frame.
This step can be called multiple times.
Only forward paging is supported, you need to cache previous pages
if you need to navigate backwards.
Use dbHasCompleted() to tell when you're done.
This method returns TRUE if no more rows are available for fetching.
Repeat the last four steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
An error is raised when issuing a query over a closed
or invalid connection,
or if the query is not a non-NA string.
An error is also raised if the syntax of the query is invalid
and all query parameters are given (by passing the params argument)
or the immediate argument is set to TRUE.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
rs <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = 4")
dbFetch(rs)
dbClearResult(rs)
# Pass one set of values with the param argument:
rs <- dbSendQuery(
con,
"SELECT * FROM mtcars WHERE cyl = ?",
params = list(4L)
)
dbFetch(rs)
dbClearResult(rs)
# Pass multiple sets of values with dbBind():
rs <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = ?")
dbBind(rs, list(6L))
dbFetch(rs)
dbBind(rs, list(8L))
dbFetch(rs)
dbClearResult(rs)
dbDisconnect(con)
This section describes the behavior of the following methods:
dbFetch(res, n = -1, ...)
fetch(res, n = -1, ...)
Fetch the next n elements (rows) from the result set and return them
as a data.frame.
res |
An object inheriting from DBIResult, created by
|
n |
maximum number of records to retrieve per fetch. Use |
... |
Other arguments passed on to methods. |
fetch() is provided for compatibility with older DBI clients - for all
new code you are strongly encouraged to use dbFetch(). The default
implementation for dbFetch() calls fetch() so that it is compatible with
existing code. Modern backends should implement for dbFetch() only.
dbFetch() always returns a data.frame with
as many rows as records were fetched and as many
columns as fields in the result set,
even if the result is a single value
or has one
or zero rows.
Passing n = NA is supported and returns an arbitrary number of rows (at least one)
as specified by the driver, but at most the remaining rows in the result set.
This section gives a complete overview over the flow for the execution of queries that return tabular data as data frames.
Most of this flow, except repeated calling of dbBind() or dbBindArrow(),
is implemented by dbGetQuery(), which should be sufficient
unless you want to access the results in a paged way
or you have a parameterized query that you want to reuse.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendQuery() to create a result set object of class
DBIResult.
Optionally, bind query parameters with dbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbColumnInfo() to retrieve the structure of the result set
without retrieving actual data.
Use dbFetch() to get the entire result set, a page of results,
or the remaining rows.
Fetching zero rows is also possible to retrieeve the structure of the result set
as a data frame.
This step can be called multiple times.
Only forward paging is supported, you need to cache previous pages
if you need to navigate backwards.
Use dbHasCompleted() to tell when you're done.
This method returns TRUE if no more rows are available for fetching.
Repeat the last four steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
An attempt to fetch from a closed result set raises an error.
If the n argument is not an atomic whole number
greater or equal to -1 or Inf, an error is raised,
but a subsequent call to dbFetch() with proper n argument succeeds.
Calling dbFetch() on a result set from a data manipulation query
created by dbSendStatement() can
be fetched and return an empty data frame, with a warning.
Fetching multi-row queries with one
or more columns by default returns the entire result.
Multi-row queries can also be fetched progressively
by passing a whole number (integer or
numeric)
as the n argument.
A value of Inf for the n argument is supported
and also returns the full result.
If more rows than available are fetched, the result is returned in full
without warning.
If fewer rows than requested are returned, further fetches will
return a data frame with zero rows.
If zero rows are fetched, the columns of the data frame are still fully
typed.
Fetching fewer rows than available is permitted,
no warning is issued when clearing the result set.
A column named row_names is treated like any other column.
The column types of the returned data frame depend on the data returned:
integer (or coercible to an integer) for integer values between -2^31 and 2^31 - 1,
with NA for SQL NULL values
numeric for numbers with a fractional component,
with NA for SQL NULL values
logical for Boolean values (some backends may return an integer);
with NA for SQL NULL values
character for text,
with NA for SQL NULL values
lists of raw for blobs with NULL entries for SQL NULL values
coercible using as.Date() for dates,
with NA for SQL NULL values
(also applies to the return value of the SQL function current_date)
coercible using hms::as_hms() for times,
with NA for SQL NULL values
(also applies to the return value of the SQL function current_time)
coercible using as.POSIXct() for timestamps,
with NA for SQL NULL values
(also applies to the return value of the SQL function current_timestamp)
If dates and timestamps are supported by the backend, the following R types are used:
Date for dates
(also applies to the return value of the SQL function current_date)
POSIXct for timestamps
(also applies to the return value of the SQL function current_timestamp)
R has no built-in type with lossless support for the full range of 64-bit or larger integers. If 64-bit integers are returned from a query, the following rules apply:
Values are returned in a container with support for the full range of
valid 64-bit values (such as the integer64 class of the bit64
package)
Coercion to numeric always returns a number that is as close as possible to the true value
Loss of precision when converting to numeric gives a warning
Conversion to character always returns a lossless decimal representation of the data
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
# Fetch all results
rs <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = 4")
dbFetch(rs)
dbClearResult(rs)
# Fetch in chunks
rs <- dbSendQuery(con, "SELECT * FROM mtcars")
while (!dbHasCompleted(rs)) {
chunk <- dbFetch(rs, 10)
print(nrow(chunk))
}
dbClearResult(rs)
dbDisconnect(con)
This section describes the behavior of the following method:
dbClearResult(res, ...)
Frees all resources (local and remote) associated with a result set.
This step is mandatory for all objects obtained by calling
dbSendQuery() or dbSendStatement().
res |
An object inheriting from DBIResult. |
... |
Other arguments passed on to methods. |
dbClearResult() returns TRUE, invisibly, for result sets obtained from
dbSendQuery(),
dbSendStatement(),
or dbSendQueryArrow(),
This section gives a complete overview over the flow for the execution of queries that return tabular data as data frames.
Most of this flow, except repeated calling of dbBind() or dbBindArrow(),
is implemented by dbGetQuery(), which should be sufficient
unless you want to access the results in a paged way
or you have a parameterized query that you want to reuse.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendQuery() to create a result set object of class
DBIResult.
Optionally, bind query parameters with dbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbColumnInfo() to retrieve the structure of the result set
without retrieving actual data.
Use dbFetch() to get the entire result set, a page of results,
or the remaining rows.
Fetching zero rows is also possible to retrieeve the structure of the result set
as a data frame.
This step can be called multiple times.
Only forward paging is supported, you need to cache previous pages
if you need to navigate backwards.
Use dbHasCompleted() to tell when you're done.
This method returns TRUE if no more rows are available for fetching.
Repeat the last four steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
This section gives a complete overview over the flow
for the execution of SQL statements that have side effects
such as stored procedures, inserting or deleting data,
or setting database or connection options.
Most of this flow, except repeated calling of dbBindArrow(),
is implemented by dbExecute(), which should be sufficient
for non-parameterized queries.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendStatement() to create a result set object of class
DBIResult.
For some queries you need to pass immediate = TRUE.
Optionally, bind query parameters withdbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbGetRowsAffected() to retrieve the number
of rows affected by the query.
Repeat the last two steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
An attempt to close an already closed result set issues a warning
for dbSendQuery(),
dbSendStatement(),
and dbSendQueryArrow(),
dbClearResult() frees all resources associated with retrieving
the result of a query or update operation.
The DBI backend can expect a call to dbClearResult() for each
dbSendQuery() or dbSendStatement() call.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
rs <- dbSendQuery(con, "SELECT 1")
print(dbFetch(rs))
dbClearResult(rs)
dbDisconnect(con)
This section describes the behavior of the following methods:
dbBind(res, params, ...)
dbBindArrow(res, params, ...)
For parametrized or prepared statements,
the dbSendQuery(), dbSendQueryArrow(), and dbSendStatement() functions
can be called with statements that contain placeholders for values.
The dbBind() and dbBindArrow() functions bind these placeholders
to actual values,
and are intended to be called on the result set
before calling dbFetch() or dbFetchArrow().
The values are passed to dbBind() as lists or data frames,
and to dbBindArrow() as a stream
created by nanoarrow::as_nanoarrow_array_stream().
dbBindArrow() is experimental, as are the other *Arrow functions.
dbSendQuery() is compatible with dbBindArrow(), and dbSendQueryArrow()
is compatible with dbBind().
res |
An object inheriting from DBIResult. |
params |
For |
... |
Other arguments passed on to methods. |
DBI supports parametrized (or prepared) queries and statements
via the dbBind() and dbBindArrow() generics.
Parametrized queries are different from normal queries
in that they allow an arbitrary number of placeholders,
which are later substituted by actual values.
Parametrized queries (and statements) serve two purposes:
The same query can be executed more than once with different values. The DBMS may cache intermediate information for the query, such as the execution plan, and execute it faster.
Separation of query syntax and parameters protects against SQL injection.
The placeholder format is currently not specified by DBI;
in the future, a uniform placeholder syntax may be supported.
Consult the backend documentation for the supported formats.
For automated testing, backend authors specify the placeholder syntax with
the placeholder_pattern tweak.
Known examples are:
? (positional matching in order of appearance) in RMariaDB and RSQLite
\$1 (positional matching by index) in RPostgres and RSQLite
:name and \$name (named matching) in RSQLite
dbBind() returns the result set,
invisibly,
for queries issued by dbSendQuery() or dbSendQueryArrow() and
also for data manipulation statements issued by
dbSendStatement().
This section gives a complete overview over the flow for the execution of queries that return tabular data as data frames.
Most of this flow, except repeated calling of dbBind() or dbBindArrow(),
is implemented by dbGetQuery(), which should be sufficient
unless you want to access the results in a paged way
or you have a parameterized query that you want to reuse.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendQuery() to create a result set object of class
DBIResult.
Optionally, bind query parameters with dbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbColumnInfo() to retrieve the structure of the result set
without retrieving actual data.
Use dbFetch() to get the entire result set, a page of results,
or the remaining rows.
Fetching zero rows is also possible to retrieeve the structure of the result set
as a data frame.
This step can be called multiple times.
Only forward paging is supported, you need to cache previous pages
if you need to navigate backwards.
Use dbHasCompleted() to tell when you're done.
This method returns TRUE if no more rows are available for fetching.
Repeat the last four steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
This section gives a complete overview over the flow for the execution of queries that return tabular data as an Arrow stream.
Most of this flow, except repeated calling of dbBindArrow() or dbBind(),
is implemented by dbGetQueryArrow(),
which should be sufficient
unless you have a parameterized query that you want to reuse.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendQueryArrow() to create a result set object of class
DBIResultArrow.
Optionally, bind query parameters with dbBindArrow() or dbBind().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Use dbFetchArrow() to get a data stream.
Repeat the last two steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
This section gives a complete overview over the flow
for the execution of SQL statements that have side effects
such as stored procedures, inserting or deleting data,
or setting database or connection options.
Most of this flow, except repeated calling of dbBindArrow(),
is implemented by dbExecute(), which should be sufficient
for non-parameterized queries.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendStatement() to create a result set object of class
DBIResult.
For some queries you need to pass immediate = TRUE.
Optionally, bind query parameters withdbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbGetRowsAffected() to retrieve the number
of rows affected by the query.
Repeat the last two steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
Calling dbBind() for a query without parameters
raises an error.
Binding too many
or not enough values,
or parameters with wrong names
or unequal length,
also raises an error.
If the placeholders in the query are named,
all parameter values must have names
(which must not be empty
or NA),
and vice versa,
otherwise an error is raised.
The behavior for mixing placeholders of different types
(in particular mixing positional and named placeholders)
is not specified.
Calling dbBind() on a result set already cleared by dbClearResult()
also raises an error.
DBI clients execute parametrized statements as follows:
Call dbSendQuery(), dbSendQueryArrow() or dbSendStatement()
with a query or statement that contains placeholders,
store the returned DBIResult object in a variable.
Mixing placeholders (in particular, named and unnamed ones) is not
recommended.
It is good practice to register a call to dbClearResult() via
on.exit() right after calling dbSendQuery() or dbSendStatement()
(see the last enumeration item).
Until dbBind() or dbBindArrow() have been called,
the returned result set object has the following behavior:
dbFetch() raises an error (for dbSendQuery() and dbSendQueryArrow())
dbGetRowCount() returns zero (for dbSendQuery() and dbSendQueryArrow())
dbGetRowsAffected() returns an integer NA (for dbSendStatement())
dbIsValid() returns TRUE
dbHasCompleted() returns FALSE
Call dbBind() or dbBindArrow():
For dbBind(), the params argument must be a list where all elements
have the same lengths and contain values supported by the backend.
A data.frame is internally stored as such a list.
For dbBindArrow(), the params argument must be a
nanoarrow array stream, with one column per query parameter.
Retrieve the data or the number of affected rows from the DBIResult object.
For queries issued by dbSendQuery() or dbSendQueryArrow(), call dbFetch().
For statements issued by dbSendStatements(),
call dbGetRowsAffected().
(Execution begins immediately after the dbBind() call,
the statement is processed entirely before the function returns.)
Repeat 2. and 3. as necessary.
Close the result set via dbClearResult().
The elements of the params argument do not need to be scalars,
vectors of arbitrary length
(including length 0)
are supported.
For queries, calling dbFetch() binding such parameters returns
concatenated results, equivalent to binding and fetching for each set
of values and connecting via rbind().
For data manipulation statements, dbGetRowsAffected() returns the
total number of rows affected if binding non-scalar parameters.
dbBind() also accepts repeated calls on the same result set
for both queries
and data manipulation statements,
even if no results are fetched between calls to dbBind(),
for both queries
and data manipulation statements.
If the placeholders in the query are named,
their order in the params argument is not important.
At least the following data types are accepted on input (including NA):
integer
numeric
logical for Boolean values
character (also with special characters such as spaces, newlines, quotes, and backslashes)
factor (bound as character, with warning)
Date (also when stored internally as integer)
POSIXct timestamps
POSIXlt timestamps
difftime values (also with units other than seconds and with the value stored as integer)
lists of raw for blobs (with NULL entries for SQL NULL values)
objects of type blob::blob
# Data frame flow:
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "iris", iris)
# Using the same query for different values
iris_result <- dbSendQuery(con, "SELECT * FROM iris WHERE [Petal.Width] > ?")
dbBind(iris_result, list(2.3))
dbFetch(iris_result)
dbBind(iris_result, list(3))
dbFetch(iris_result)
dbClearResult(iris_result)
# Executing the same statement with different values at once
iris_result <- dbSendStatement(con, "DELETE FROM iris WHERE [Species] = \$species")
dbBind(iris_result, list(species = c("setosa", "versicolor", "unknown")))
dbGetRowsAffected(iris_result)
dbClearResult(iris_result)
nrow(dbReadTable(con, "iris"))
dbDisconnect(con)
# Arrow flow:
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "iris", iris)
# Using the same query for different values
iris_result <- dbSendQueryArrow(con, "SELECT * FROM iris WHERE [Petal.Width] > ?")
dbBindArrow(
iris_result,
nanoarrow::as_nanoarrow_array_stream(data.frame(2.3, fix.empty.names = FALSE))
)
as.data.frame(dbFetchArrow(iris_result))
dbBindArrow(
iris_result,
nanoarrow::as_nanoarrow_array_stream(data.frame(3, fix.empty.names = FALSE))
)
as.data.frame(dbFetchArrow(iris_result))
dbClearResult(iris_result)
# Executing the same statement with different values at once
iris_result <- dbSendStatement(con, "DELETE FROM iris WHERE [Species] = \$species")
dbBindArrow(iris_result, nanoarrow::as_nanoarrow_array_stream(data.frame(
species = c("setosa", "versicolor", "unknown")
)))
dbGetRowsAffected(iris_result)
dbClearResult(iris_result)
nrow(dbReadTable(con, "iris"))
dbDisconnect(con)
This section describes the behavior of the following method:
dbGetQuery(conn, statement, ...)
Returns the result of a query as a data frame.
dbGetQuery() comes with a default implementation
(which should work with most backends) that calls
dbSendQuery(), then dbFetch(), ensuring that
the result is always freed by dbClearResult().
For retrieving chunked/paged results or for passing query parameters,
see dbSendQuery(), in particular the "The data retrieval flow" section.
For retrieving results as an Arrow object, see dbGetQueryArrow().
conn |
A DBIConnection object, as returned by
|
statement |
a character string containing SQL. |
... |
Other parameters passed on to methods. |
The following arguments are not part of the dbGetQuery() generic
(to improve compatibility across backends)
but are part of the DBI specification:
n (default: -1)
params (default: NULL)
immediate (default: NULL)
They must be provided as named arguments. See the "Specification" and "Value" sections for details on their usage.
A column named row_names is treated like any other column.
The n argument specifies the number of rows to be fetched.
If omitted, fetching multi-row queries with one
or more columns returns the entire result.
A value of Inf for the n argument is supported
and also returns the full result.
If more rows than available are fetched (by passing a too large value for
n), the result is returned in full without warning.
If zero rows are requested, the columns of the data frame are still fully
typed.
Fetching fewer rows than available is permitted,
no warning is issued.
The param argument allows passing query parameters, see dbBind() for details.
immediate argumentThe immediate argument supports distinguishing between "direct"
and "prepared" APIs offered by many database drivers.
Passing immediate = TRUE leads to immediate execution of the
query or statement, via the "direct" API (if supported by the driver).
The default NULL means that the backend should choose whatever API
makes the most sense for the database, and (if relevant) tries the
other API if the first attempt fails. A successful second attempt
should result in a message that suggests passing the correct
immediate argument.
Examples for possible behaviors:
DBI backend defaults to immediate = TRUE internally
A query without parameters is passed: query is executed
A query with parameters is passed:
params not given: rejected immediately by the database
because of a syntax error in the query, the backend tries
immediate = FALSE (and gives a message)
params given: query is executed using immediate = FALSE
DBI backend defaults to immediate = FALSE internally
A query without parameters is passed:
simple query: query is executed
"special" query (such as setting a config options): fails,
the backend tries immediate = TRUE (and gives a message)
A query with parameters is passed:
params not given: waiting for parameters via dbBind()
params given: query is executed
This method is for SELECT queries only
(incl. other SQL statements that return a SELECT-alike result,
e.g., execution of a stored procedure or data manipulation queries
like INSERT INTO ... RETURNING ...).
To execute a stored procedure that does not return a result set,
use dbExecute().
Some backends may
support data manipulation statements through this method for compatibility
reasons. However, callers are strongly advised to use
dbExecute() for data manipulation statements.
dbGetQuery() always returns a data.frame, with
as many rows as records were fetched and as many
columns as fields in the result set,
even if the result is a single value
or has one
or zero rows.
Subclasses should override this method only if they provide some sort of performance optimization.
An error is raised when issuing a query over a closed
or invalid connection,
if the syntax of the query is invalid,
or if the query is not a non-NA string.
If the n argument is not an atomic whole number
greater or equal to -1 or Inf, an error is raised,
but a subsequent call to dbGetQuery() with proper n argument succeeds.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
dbGetQuery(con, "SELECT * FROM mtcars")
dbGetQuery(con, "SELECT * FROM mtcars", n = 6)
# Pass values using the param argument:
# (This query runs eight times, once for each different
# parameter. The resulting rows are combined into a single
# data frame.)
dbGetQuery(
con,
"SELECT COUNT(*) FROM mtcars WHERE cyl = ?",
params = list(1:8)
)
dbDisconnect(con)
This section describes the behavior of the following method:
dbSendStatement(conn, statement, ...)
The dbSendStatement() method only submits and synchronously executes the
SQL data manipulation statement (e.g., UPDATE, DELETE,
INSERT INTO, DROP TABLE, ...) to the database engine. To query
the number of affected rows, call dbGetRowsAffected() on the
returned result object. You must also call dbClearResult() after
that. For interactive use, you should almost always prefer
dbExecute().
conn |
A DBIConnection object, as returned by
|
statement |
a character string containing SQL. |
... |
Other parameters passed on to methods. |
The following arguments are not part of the dbSendStatement() generic
(to improve compatibility across backends)
but are part of the DBI specification:
params (default: NULL)
immediate (default: NULL)
They must be provided as named arguments. See the "Specification" sections for details on their usage.
No warnings occur under normal conditions.
When done, the DBIResult object must be cleared with a call to
dbClearResult().
Failure to clear the result set leads to a warning
when the connection is closed.
If the backend supports only one open result set per connection,
issuing a second query invalidates an already open result set
and raises a warning.
The newly opened result set is valid
and must be cleared with dbClearResult().
The param argument allows passing query parameters, see dbBind() for details.
immediate argumentThe immediate argument supports distinguishing between "direct"
and "prepared" APIs offered by many database drivers.
Passing immediate = TRUE leads to immediate execution of the
query or statement, via the "direct" API (if supported by the driver).
The default NULL means that the backend should choose whatever API
makes the most sense for the database, and (if relevant) tries the
other API if the first attempt fails. A successful second attempt
should result in a message that suggests passing the correct
immediate argument.
Examples for possible behaviors:
DBI backend defaults to immediate = TRUE internally
A query without parameters is passed: query is executed
A query with parameters is passed:
params not given: rejected immediately by the database
because of a syntax error in the query, the backend tries
immediate = FALSE (and gives a message)
params given: query is executed using immediate = FALSE
DBI backend defaults to immediate = FALSE internally
A query without parameters is passed:
simple query: query is executed
"special" query (such as setting a config options): fails,
the backend tries immediate = TRUE (and gives a message)
A query with parameters is passed:
params not given: waiting for parameters via dbBind()
params given: query is executed
dbSendStatement() comes with a default implementation that simply
forwards to dbSendQuery(), to support backends that only
implement the latter.
dbSendStatement() returns
an S4 object that inherits from DBIResult.
The result set can be used with dbGetRowsAffected() to
determine the number of rows affected by the query.
Once you have finished using a result, make sure to clear it
with dbClearResult().
This section gives a complete overview over the flow
for the execution of SQL statements that have side effects
such as stored procedures, inserting or deleting data,
or setting database or connection options.
Most of this flow, except repeated calling of dbBindArrow(),
is implemented by dbExecute(), which should be sufficient
for non-parameterized queries.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendStatement() to create a result set object of class
DBIResult.
For some queries you need to pass immediate = TRUE.
Optionally, bind query parameters withdbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbGetRowsAffected() to retrieve the number
of rows affected by the query.
Repeat the last two steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
An error is raised when issuing a statement over a closed
or invalid connection,
or if the statement is not a non-NA string.
An error is also raised if the syntax of the query is invalid
and all query parameters are given (by passing the params argument)
or the immediate argument is set to TRUE.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "cars", head(cars, 3))
rs <- dbSendStatement(
con,
"INSERT INTO cars (speed, dist) VALUES (1, 1), (2, 2), (3, 3)"
)
dbHasCompleted(rs)
dbGetRowsAffected(rs)
dbClearResult(rs)
dbReadTable(con, "cars") # there are now 6 rows
# Pass one set of values directly using the param argument:
rs <- dbSendStatement(
con,
"INSERT INTO cars (speed, dist) VALUES (?, ?)",
params = list(4L, 5L)
)
dbClearResult(rs)
# Pass multiple sets of values using dbBind():
rs <- dbSendStatement(
con,
"INSERT INTO cars (speed, dist) VALUES (?, ?)"
)
dbBind(rs, list(5:6, 6:7))
dbBind(rs, list(7L, 8L))
dbClearResult(rs)
dbReadTable(con, "cars") # there are now 10 rows
dbDisconnect(con)
This section describes the behavior of the following method:
dbExecute(conn, statement, ...)
Executes a statement and returns the number of rows affected.
dbExecute() comes with a default implementation
(which should work with most backends) that calls
dbSendStatement(), then dbGetRowsAffected(), ensuring that
the result is always freed by dbClearResult().
For passing query parameters, see dbBind(), in particular
the "The command execution flow" section.
conn |
A DBIConnection object, as returned by
|
statement |
a character string containing SQL. |
... |
Other parameters passed on to methods. |
The following arguments are not part of the dbExecute() generic
(to improve compatibility across backends)
but are part of the DBI specification:
params (default: NULL)
immediate (default: NULL)
They must be provided as named arguments. See the "Specification" sections for details on their usage.
The param argument allows passing query parameters, see dbBind() for details.
immediate argumentThe immediate argument supports distinguishing between "direct"
and "prepared" APIs offered by many database drivers.
Passing immediate = TRUE leads to immediate execution of the
query or statement, via the "direct" API (if supported by the driver).
The default NULL means that the backend should choose whatever API
makes the most sense for the database, and (if relevant) tries the
other API if the first attempt fails. A successful second attempt
should result in a message that suggests passing the correct
immediate argument.
Examples for possible behaviors:
DBI backend defaults to immediate = TRUE internally
A query without parameters is passed: query is executed
A query with parameters is passed:
params not given: rejected immediately by the database
because of a syntax error in the query, the backend tries
immediate = FALSE (and gives a message)
params given: query is executed using immediate = FALSE
DBI backend defaults to immediate = FALSE internally
A query without parameters is passed:
simple query: query is executed
"special" query (such as setting a config options): fails,
the backend tries immediate = TRUE (and gives a message)
A query with parameters is passed:
params not given: waiting for parameters via dbBind()
params given: query is executed
You can also use dbExecute() to call a stored procedure
that performs data manipulation or other actions that do not return a result set.
To execute a stored procedure that returns a result set,
or a data manipulation query that also returns a result set
such as INSERT INTO ... RETURNING ..., use dbGetQuery() instead.
dbExecute() always returns a
scalar
numeric
that specifies the number of rows affected
by the statement.
Subclasses should override this method only if they provide some sort of performance optimization.
An error is raised when issuing a statement over a closed
or invalid connection,
if the syntax of the statement is invalid,
or if the statement is not a non-NA string.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "cars", head(cars, 3))
dbReadTable(con, "cars") # there are 3 rows
dbExecute(
con,
"INSERT INTO cars (speed, dist) VALUES (1, 1), (2, 2), (3, 3)"
)
dbReadTable(con, "cars") # there are now 6 rows
# Pass values using the param argument:
dbExecute(
con,
"INSERT INTO cars (speed, dist) VALUES (?, ?)",
params = list(4:7, 5:8)
)
dbReadTable(con, "cars") # there are now 10 rows
dbDisconnect(con)
This section describes the behavior of the following method:
dbQuoteString(conn, x, ...)
Call this method to generate a string that is suitable for use in a query as a string literal, to make sure that you generate valid SQL and protect against SQL injection attacks.
conn |
A DBIConnection object, as returned by
|
x |
A character vector to quote as string. |
... |
Other arguments passed on to methods. |
dbQuoteString() returns an object that can be coerced to character,
of the same length as the input.
For an empty character vector this function returns a length-0 object.
When passing the returned object again to dbQuoteString()
as x
argument, it is returned unchanged.
Passing objects of class SQL should also return them unchanged.
(For backends it may be most convenient to return SQL objects
to achieve this behavior, but this is not required.)
Passing a numeric,
integer,
logical,
or raw vector,
or a list
for the x argument raises an error.
The returned expression can be used in a SELECT ... query,
and for any scalar character x the value of
dbGetQuery(paste0("SELECT ", dbQuoteString(x)))[[1]]
must be identical to x,
even if x contains
spaces,
tabs,
quotes (single
or double),
backticks,
or newlines
(in any combination)
or is itself the result of a dbQuoteString() call coerced back to
character (even repeatedly).
If x is NA, the result must merely satisfy is.na().
The strings "NA" or "NULL" are not treated specially.
NA should be translated to an unquoted SQL NULL,
so that the query SELECT * FROM (SELECT 1) a WHERE ... IS NULL
returns one row.
# Quoting ensures that arbitrary input is safe for use in a query
name <- "Robert'); DROP TABLE Students;--"
dbQuoteString(ANSI(), name)
# NAs become NULL
dbQuoteString(ANSI(), c("x", NA))
# SQL vectors are always passed through as is
var_name <- SQL("select")
var_name
dbQuoteString(ANSI(), var_name)
# This mechanism is used to prevent double escaping
dbQuoteString(ANSI(), dbQuoteString(ANSI(), name))
This section describes the behavior of the following method:
dbQuoteIdentifier(conn, x, ...)
Call this method to generate a string that is suitable for
use in a query as a column or table name, to make sure that you
generate valid SQL and protect against SQL injection attacks. The inverse
operation is dbUnquoteIdentifier().
conn |
A DBIConnection object, as returned by
|
x |
A character vector, SQL or Id object to quote as identifier. |
... |
Other arguments passed on to methods. |
dbQuoteIdentifier() returns an object that can be coerced to character,
of the same length as the input.
For an empty character vector this function returns a length-0 object.
The names of the input argument are preserved in the output.
When passing the returned object again to dbQuoteIdentifier()
as x
argument, it is returned unchanged.
Passing objects of class SQL should also return them unchanged.
(For backends it may be most convenient to return SQL objects
to achieve this behavior, but this is not required.)
An error is raised if the input contains NA,
but not for an empty string.
Calling dbGetQuery() for a query of the format SELECT 1 AS ...
returns a data frame with the identifier, unquoted, as column name.
Quoted identifiers can be used as table and column names in SQL queries,
in particular in queries like SELECT 1 AS ...
and SELECT * FROM (SELECT 1) ....
The method must use a quoting mechanism that is unambiguously different
from the quoting mechanism used for strings, so that a query like
SELECT ... FROM (SELECT 1 AS ...)
throws an error if the column names do not match.
The method can quote column names that
contain special characters such as a space,
a dot,
a comma,
or quotes used to mark strings
or identifiers,
if the database supports this.
In any case, checking the validity of the identifier
should be performed only when executing a query,
and not by dbQuoteIdentifier().
# Quoting ensures that arbitrary input is safe for use in a query
name <- "Robert'); DROP TABLE Students;--"
dbQuoteIdentifier(ANSI(), name)
# Use Id() to specify other components such as the schema
id_name <- Id(schema = "schema_name", table = "table_name")
id_name
dbQuoteIdentifier(ANSI(), id_name)
# SQL vectors are always passed through as is
var_name <- SQL("select")
var_name
dbQuoteIdentifier(ANSI(), var_name)
# This mechanism is used to prevent double escaping
dbQuoteIdentifier(ANSI(), dbQuoteIdentifier(ANSI(), name))
This section describes the behavior of the following method:
dbReadTable(conn, name, ...)
Reads a database table to a data frame, optionally converting
a column to row names and converting the column names to valid
R identifiers.
Use dbReadTableArrow() instead to obtain an Arrow object.
conn |
A DBIConnection object, as returned by
|
name |
The table name, passed on to
|
... |
Other parameters passed on to methods. |
The following arguments are not part of the dbReadTable() generic
(to improve compatibility across backends)
but are part of the DBI specification:
row.names (default: FALSE)
check.names
They must be provided as named arguments. See the "Value" section for details on their usage.
The name argument is processed as follows,
to support databases that allow non-syntactic names for their objects:
If an unquoted table name as string: dbReadTable() will do the
quoting,
perhaps by calling dbQuoteIdentifier(conn, x = name)
If the result of a call to dbQuoteIdentifier(): no more quoting is done
This function returns a data frame.
Use dbReadTableArrow() to obtain an Arrow object.
dbReadTable() returns a data frame that contains the complete data
from the remote table, effectively the result of calling dbGetQuery() with
SELECT * FROM <name>.
An empty table is returned as a data frame with zero rows.
The presence of rownames depends on the row.names argument,
see sqlColumnToRownames() for details:
If FALSE or NULL, the returned data frame doesn't have row names.
If TRUE, a column named "row_names" is converted to row names.
If NA, a column named "row_names" is converted to row names if it exists,
otherwise no translation occurs.
If a string, this specifies the name of the column in the remote table that contains the row names.
The default is row.names = FALSE.
If the database supports identifiers with special characters,
the columns in the returned data frame are converted to valid R
identifiers
if the check.names argument is TRUE,
If check.names = FALSE, the returned table has non-syntactic column names without quotes.
An error is raised if the table does not exist.
An error is raised if row.names is TRUE and no "row_names" column exists,
An error is raised if row.names is set to a string and no corresponding column exists.
An error is raised when calling this method for a closed
or invalid connection.
An error is raised
if name cannot be processed with dbQuoteIdentifier()
or if this results in a non-scalar.
Unsupported values for row.names and check.names
(non-scalars,
unsupported data types,
NA for check.names)
also raise an error.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars[1:10, ])
dbReadTable(con, "mtcars")
dbDisconnect(con)
This section describes the behavior of the following method:
dbWriteTable(conn, name, value, ...)
Writes, overwrites or appends a data frame to a database table, optionally converting row names to a column and specifying SQL data types for fields.
conn |
A DBIConnection object, as returned by
|
name |
The table name, passed on to
|
value |
A data.frame (or coercible to data.frame). |
... |
Other parameters passed on to methods. |
The following arguments are not part of the dbWriteTable() generic
(to improve compatibility across backends)
but are part of the DBI specification:
row.names (default: FALSE)
overwrite (default: FALSE)
append (default: FALSE)
field.types (default: NULL)
temporary (default: FALSE)
They must be provided as named arguments. See the "Specification" and "Value" sections for details on their usage.
The name argument is processed as follows,
to support databases that allow non-syntactic names for their objects:
If an unquoted table name as string: dbWriteTable() will do the quoting,
perhaps by calling dbQuoteIdentifier(conn, x = name)
If the result of a call to dbQuoteIdentifier(): no more quoting is done
The value argument must be a data frame
with a subset of the columns of the existing table if append = TRUE.
The order of the columns does not matter with append = TRUE.
If the overwrite argument is TRUE, an existing table of the same name
will be overwritten.
This argument doesn't change behavior if the table does not exist yet.
If the append argument is TRUE, the rows in an existing table are
preserved, and the new data are appended.
If the table doesn't exist yet, it is created.
If the temporary argument is TRUE, the table is not available in a
second connection and is gone after reconnecting.
Not all backends support this argument.
A regular, non-temporary table is visible in a second connection,
in a pre-existing connection,
and after reconnecting to the database.
SQL keywords can be used freely in table names, column names, and data. Quotes, commas, spaces, and other special characters such as newlines and tabs, can also be used in the data, and, if the database supports non-syntactic identifiers, also for table names and column names.
The following data types must be supported at least,
and be read identically with dbReadTable():
integer
numeric
(the behavior for Inf and NaN is not specified)
logical
NA as NULL
64-bit values (using "bigint" as field type); the result can be
converted to a numeric, which may lose precision,
converted a character vector, which gives the full decimal representation
written to another table and read again unchanged
character (in both UTF-8 and native encodings), supporting empty strings before and after a non-empty string
factor (returned as character)
list of raw (if supported by the database)
objects of type blob::blob (if supported by the database)
date
(if supported by the database;
returned as Date),
also for dates prior to 1970 or 1900 or after 2038
time
(if supported by the database;
returned as objects that inherit from difftime)
timestamp
(if supported by the database;
returned as POSIXct
respecting the time zone but not necessarily preserving the
input time zone),
also for timestamps prior to 1970 or 1900 or after 2038
respecting the time zone but not necessarily preserving the
input time zone)
Mixing column types in the same table is supported.
The field.types argument must be a named character vector with at most
one entry for each column.
It indicates the SQL data type to be used for a new column.
If a column is missed from field.types, the type is inferred
from the input data with dbDataType().
The interpretation of rownames depends on the row.names argument,
see sqlRownamesToColumn() for details:
If FALSE or NULL, row names are ignored.
If TRUE, row names are converted to a column named "row_names",
even if the input data frame only has natural row names from 1 to nrow(...).
If NA, a column named "row_names" is created if the data has custom row names,
no extra column is created in the case of natural row names.
If a string, this specifies the name of the column in the remote table that contains the row names, even if the input data frame only has natural row names.
The default is row.names = FALSE.
This function expects a data frame.
Use dbWriteTableArrow() to write an Arrow object.
This function is useful if you want to create and load a table at the same time.
Use dbAppendTable() or dbAppendTableArrow() for appending data to an existing
table, dbCreateTable() or dbCreateTableArrow() for creating a table,
and dbExistsTable() and dbRemoveTable() for overwriting tables.
DBI only standardizes writing data frames with dbWriteTable().
Some backends might implement methods that can consume CSV files
or other data formats.
For details, see the documentation for the individual methods.
dbWriteTable() returns TRUE, invisibly.
If the table exists, and both append and overwrite arguments are unset,
or append = TRUE and the data frame with the new data has different
column names,
an error is raised; the remote table remains unchanged.
An error is raised when calling this method for a closed
or invalid connection.
An error is also raised
if name cannot be processed with dbQuoteIdentifier() or
if this results in a non-scalar.
Invalid values for the additional arguments row.names,
overwrite, append, field.types, and temporary
(non-scalars,
unsupported data types,
NA,
incompatible values,
duplicate
or missing names,
incompatible columns)
also raise an error.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars[1:5, ])
dbReadTable(con, "mtcars")
dbWriteTable(con, "mtcars", mtcars[6:10, ], append = TRUE)
dbReadTable(con, "mtcars")
dbWriteTable(con, "mtcars", mtcars[1:10, ], overwrite = TRUE)
dbReadTable(con, "mtcars")
# No row names
dbWriteTable(con, "mtcars", mtcars[1:10, ], overwrite = TRUE, row.names = FALSE)
dbReadTable(con, "mtcars")
This section describes the behavior of the following method:
dbListTables(conn, ...)
Returns the unquoted names of remote tables accessible through this connection. This should include views and temporary objects, but not all database backends (in particular RMariaDB and RMySQL) support this.
conn |
A DBIConnection object, as returned by
|
... |
Other parameters passed on to methods. |
dbListTables()
returns a character vector
that enumerates all tables
and views
in the database.
Tables added with dbWriteTable() are
part of the list.
As soon a table is removed from the database,
it is also removed from the list of database tables.
The same applies to temporary tables if supported by the database.
The returned names are suitable for quoting with dbQuoteIdentifier().
An error is raised when calling this method for a closed or invalid connection.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbListTables(con)
dbWriteTable(con, "mtcars", mtcars)
dbListTables(con)
dbDisconnect(con)
This section describes the behavior of the following method:
dbExistsTable(conn, name, ...)
Returns if a table given by name exists in the database.
conn |
A DBIConnection object, as returned by
|
name |
The table name, passed on to
|
... |
Other parameters passed on to methods. |
dbExistsTable() returns a logical scalar, TRUE if the table or view
specified by the name argument exists, FALSE otherwise.
This includes temporary tables if supported by the database.
An error is raised when calling this method for a closed
or invalid connection.
An error is also raised
if name cannot be processed with dbQuoteIdentifier() or
if this results in a non-scalar.
The name argument is processed as follows,
to support databases that allow non-syntactic names for their objects:
If an unquoted table name as string: dbExistsTable() will do the
quoting,
perhaps by calling dbQuoteIdentifier(conn, x = name)
If the result of a call to dbQuoteIdentifier(): no more quoting is done
For all tables listed by dbListTables(), dbExistsTable() returns TRUE.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbExistsTable(con, "iris")
dbWriteTable(con, "iris", iris)
dbExistsTable(con, "iris")
dbDisconnect(con)
This section describes the behavior of the following method:
dbRemoveTable(conn, name, ...)
Remove a remote table (e.g., created by dbWriteTable())
from the database.
conn |
A DBIConnection object, as returned by
|
name |
The table name, passed on to
|
... |
Other parameters passed on to methods. |
The following arguments are not part of the dbRemoveTable() generic
(to improve compatibility across backends)
but are part of the DBI specification:
temporary (default: FALSE)
fail_if_missing (default: TRUE)
These arguments must be provided as named arguments.
If temporary is TRUE, the call to dbRemoveTable()
will consider only temporary tables.
Not all backends support this argument.
In particular, permanent tables of the same name are left untouched.
If fail_if_missing is FALSE, the call to dbRemoveTable()
succeeds if the table does not exist.
A table removed by dbRemoveTable() doesn't appear in the list of tables
returned by dbListTables(),
and dbExistsTable() returns FALSE.
The removal propagates immediately to other connections to the same database.
This function can also be used to remove a temporary table.
The name argument is processed as follows,
to support databases that allow non-syntactic names for their objects:
If an unquoted table name as string: dbRemoveTable() will do the
quoting,
perhaps by calling dbQuoteIdentifier(conn, x = name)
If the result of a call to dbQuoteIdentifier(): no more quoting is done
dbRemoveTable() returns TRUE, invisibly.
If the table does not exist, an error is raised. An attempt to remove a view with this function may result in an error.
An error is raised when calling this method for a closed
or invalid connection.
An error is also raised
if name cannot be processed with dbQuoteIdentifier() or
if this results in a non-scalar.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbExistsTable(con, "iris")
dbWriteTable(con, "iris", iris)
dbExistsTable(con, "iris")
dbRemoveTable(con, "iris")
dbExistsTable(con, "iris")
dbDisconnect(con)
This section describes the behavior of the following method:
dbListFields(conn, name, ...)
Returns the field names of a remote table as a character vector.
conn |
A DBIConnection object, as returned by
|
name |
The table name, passed on to
|
... |
Other parameters passed on to methods. |
dbListFields()
returns a character vector
that enumerates all fields
in the table in the correct order.
This also works for temporary tables if supported by the database.
The returned names are suitable for quoting with dbQuoteIdentifier().
If the table does not exist, an error is raised.
Invalid types for the name argument
(e.g., character of length not equal to one,
or numeric)
lead to an error.
An error is also raised when calling this method for a closed
or invalid connection.
The name argument can be
a string
the return value of dbQuoteIdentifier()
a value from the table column from the return value of
dbListObjects() where is_prefix is FALSE
A column named row_names is treated like any other column.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
dbListFields(con, "mtcars")
dbDisconnect(con)
This section describes the behavior of the following method:
dbIsValid(dbObj, ...)
This generic tests whether a database object is still valid (i.e. it hasn't been disconnected or cleared).
dbObj |
An object inheriting from DBIObject, i.e. DBIDriver, DBIConnection, or a DBIResult |
... |
Other arguments to methods. |
dbIsValid() returns a logical scalar,
TRUE if the object specified by dbObj is valid,
FALSE otherwise.
A DBIConnection object is initially valid,
and becomes invalid after disconnecting with dbDisconnect().
For an invalid connection object (e.g., for some drivers if the object
is saved to a file and then restored), the method also returns FALSE.
A DBIResult object is valid after a call to dbSendQuery(),
and stays valid even after all rows have been fetched;
only clearing it with dbClearResult() invalidates it.
A DBIResult object is also valid after a call to dbSendStatement(),
and stays valid after querying the number of rows affected;
only clearing it with dbClearResult() invalidates it.
If the connection to the database system is dropped (e.g., due to
connectivity problems, server failure, etc.), dbIsValid() should return
FALSE. This is not tested automatically.
dbIsValid(RSQLite::SQLite())
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbIsValid(con)
rs <- dbSendQuery(con, "SELECT 1")
dbIsValid(rs)
dbClearResult(rs)
dbIsValid(rs)
dbDisconnect(con)
dbIsValid(con)
This section describes the behavior of the following method:
dbHasCompleted(res, ...)
This method returns if the operation has completed.
A SELECT query is completed if all rows have been fetched.
A data manipulation statement is always completed.
res |
An object inheriting from DBIResult. |
... |
Other arguments passed on to methods. |
dbHasCompleted() returns a logical scalar.
For a query initiated by dbSendQuery() with non-empty result set,
dbHasCompleted() returns FALSE initially
and TRUE after calling dbFetch() without limit.
For a query initiated by dbSendStatement(),
dbHasCompleted() always returns TRUE.
This section gives a complete overview over the flow for the execution of queries that return tabular data as data frames.
Most of this flow, except repeated calling of dbBind() or dbBindArrow(),
is implemented by dbGetQuery(), which should be sufficient
unless you want to access the results in a paged way
or you have a parameterized query that you want to reuse.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendQuery() to create a result set object of class
DBIResult.
Optionally, bind query parameters with dbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbColumnInfo() to retrieve the structure of the result set
without retrieving actual data.
Use dbFetch() to get the entire result set, a page of results,
or the remaining rows.
Fetching zero rows is also possible to retrieeve the structure of the result set
as a data frame.
This step can be called multiple times.
Only forward paging is supported, you need to cache previous pages
if you need to navigate backwards.
Use dbHasCompleted() to tell when you're done.
This method returns TRUE if no more rows are available for fetching.
Repeat the last four steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
Attempting to query completion status for a result set cleared with
dbClearResult() gives an error.
The completion status for a query is only guaranteed to be set to
FALSE after attempting to fetch past the end of the entire result.
Therefore, for a query with an empty result set,
the initial return value is unspecified,
but the result value is TRUE after trying to fetch only one row.
Similarly, for a query with a result set of length n,
the return value is unspecified after fetching n rows,
but the result value is TRUE after trying to fetch only one more
row.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
rs <- dbSendQuery(con, "SELECT * FROM mtcars")
dbHasCompleted(rs)
ret1 <- dbFetch(rs, 10)
dbHasCompleted(rs)
ret2 <- dbFetch(rs)
dbHasCompleted(rs)
dbClearResult(rs)
dbDisconnect(con)
This section describes the behavior of the following method:
dbGetStatement(res, ...)
Returns the statement that was passed to dbSendQuery()
or dbSendStatement().
res |
An object inheriting from DBIResult. |
... |
Other arguments passed on to methods. |
dbGetStatement() returns a string, the query used in
either dbSendQuery() or
dbSendStatement().
Attempting to query the statement for a result set cleared with
dbClearResult() gives an error.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
rs <- dbSendQuery(con, "SELECT * FROM mtcars")
dbGetStatement(rs)
dbClearResult(rs)
dbDisconnect(con)
This section describes the behavior of the following method:
dbGetRowCount(res, ...)
Returns the total number of rows actually fetched with calls to dbFetch()
for this result set.
res |
An object inheriting from DBIResult. |
... |
Other arguments passed on to methods. |
dbGetRowCount() returns a scalar number (integer or numeric),
the number of rows fetched so far.
After calling dbSendQuery(),
the row count is initially zero.
After a call to dbFetch() without limit,
the row count matches the total number of rows returned.
Fetching a limited number of rows
increases the number of rows by the number of rows returned,
even if fetching past the end of the result set.
For queries with an empty result set,
zero is returned
even after fetching.
For data manipulation statements issued with
dbSendStatement(),
zero is returned before
and after calling dbFetch().
Attempting to get the row count for a result set cleared with
dbClearResult() gives an error.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
rs <- dbSendQuery(con, "SELECT * FROM mtcars")
dbGetRowCount(rs)
ret1 <- dbFetch(rs, 10)
dbGetRowCount(rs)
ret2 <- dbFetch(rs)
dbGetRowCount(rs)
nrow(ret1) + nrow(ret2)
dbClearResult(rs)
dbDisconnect(con)
This section describes the behavior of the following method:
dbGetRowsAffected(res, ...)
This method returns the number of rows that were added, deleted, or updated by a data manipulation statement.
res |
An object inheriting from DBIResult. |
... |
Other arguments passed on to methods. |
dbGetRowsAffected() returns a scalar number (integer or numeric),
the number of rows affected by a data manipulation statement
issued with dbSendStatement().
The value is available directly after the call
and does not change after calling dbFetch().
NA_integer_ or NA_numeric_ are allowed if the number of rows affected is not known.
For queries issued with dbSendQuery(),
zero is returned before
and after the call to dbFetch().
NA values are not allowed.
This section gives a complete overview over the flow
for the execution of SQL statements that have side effects
such as stored procedures, inserting or deleting data,
or setting database or connection options.
Most of this flow, except repeated calling of dbBindArrow(),
is implemented by dbExecute(), which should be sufficient
for non-parameterized queries.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendStatement() to create a result set object of class
DBIResult.
For some queries you need to pass immediate = TRUE.
Optionally, bind query parameters withdbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbGetRowsAffected() to retrieve the number
of rows affected by the query.
Repeat the last two steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
Attempting to get the rows affected for a result set cleared with
dbClearResult() gives an error.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
rs <- dbSendStatement(con, "DELETE FROM mtcars")
dbGetRowsAffected(rs)
nrow(mtcars)
dbClearResult(rs)
dbDisconnect(con)
This section describes the behavior of the following method:
dbColumnInfo(res, ...)
Produces a data.frame that describes the output of a query. The data.frame should have as many rows as there are output fields in the result set, and each column in the data.frame describes an aspect of the result set field (field name, type, etc.)
res |
An object inheriting from DBIResult. |
... |
Other arguments passed on to methods. |
dbColumnInfo()
returns a data frame
with at least two columns "name" and "type" (in that order)
(and optional columns that start with a dot).
The "name" and "type" columns contain the names and types
of the R columns of the data frame that is returned from dbFetch().
The "type" column is of type character and only for information.
Do not compute on the "type" column, instead use dbFetch(res, n = 0)
to create a zero-row data frame initialized with the correct data types.
This section gives a complete overview over the flow for the execution of queries that return tabular data as data frames.
Most of this flow, except repeated calling of dbBind() or dbBindArrow(),
is implemented by dbGetQuery(), which should be sufficient
unless you want to access the results in a paged way
or you have a parameterized query that you want to reuse.
This flow requires an active connection established by dbConnect().
See also vignette("dbi-advanced") for a walkthrough.
Use dbSendQuery() to create a result set object of class
DBIResult.
Optionally, bind query parameters with dbBind() or dbBindArrow().
This is required only if the query contains placeholders
such as ? or \$1, depending on the database backend.
Optionally, use dbColumnInfo() to retrieve the structure of the result set
without retrieving actual data.
Use dbFetch() to get the entire result set, a page of results,
or the remaining rows.
Fetching zero rows is also possible to retrieeve the structure of the result set
as a data frame.
This step can be called multiple times.
Only forward paging is supported, you need to cache previous pages
if you need to navigate backwards.
Use dbHasCompleted() to tell when you're done.
This method returns TRUE if no more rows are available for fetching.
Repeat the last four steps as necessary.
Use dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occurred during the processing.
It is good practice to use on.exit() or withr::defer()
to ensure that this step is always executed.
An attempt to query columns for a closed result set raises an error.
A column named row_names is treated like any other column.
The column names are always consistent
with the data returned by dbFetch().
If the query returns unnamed columns,
non-empty and non-NA names are assigned.
Column names that correspond to SQL or R keywords are left unchanged.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
rs <- dbSendQuery(con, "SELECT 1 AS a, 2 AS b")
dbColumnInfo(rs)
dbFetch(rs)
dbClearResult(rs)
dbDisconnect(con)
This section describes the behavior of the following methods:
dbBegin(conn, ...)
dbCommit(conn, ...)
dbRollback(conn, ...)
A transaction encapsulates several SQL statements in an atomic unit.
It is initiated with dbBegin() and either made persistent with dbCommit()
or undone with dbRollback().
In any case, the DBMS guarantees that either all or none of the statements
have a permanent effect.
This helps ensuring consistency of write operations to multiple tables.
conn |
A DBIConnection object, as returned by
|
... |
Other parameters passed on to methods. |
Not all database engines implement transaction management, in which case these methods should not be implemented for the specific DBIConnection subclass.
dbBegin(), dbCommit() and dbRollback() return TRUE, invisibly.
The implementations are expected to raise an error in case of failure,
but this is not tested.
In any way, all generics throw an error with a closed
or invalid connection.
In addition, a call to dbCommit()
or dbRollback()
without a prior call to dbBegin() raises an error.
Nested transactions are not supported by DBI,
an attempt to call dbBegin() twice
yields an error.
Actual support for transactions may vary between backends.
A transaction is initiated by a call to dbBegin()
and committed by a call to dbCommit().
Data written in a transaction must persist after the transaction is committed.
For example, a record that is missing when the transaction is started
but is created during the transaction
must exist
both during
and after the transaction,
and also in a new connection.
A transaction
can also be aborted with dbRollback().
All data written in such a transaction must be removed after the
transaction is rolled back.
For example, a record that is missing when the transaction is started
but is created during the transaction
must not exist anymore after the rollback.
Disconnection from a connection with an open transaction effectively rolls back the transaction. All data written in such a transaction must be removed after the transaction is rolled back.
The behavior is not specified if other arguments are passed to these
functions. In particular, RSQLite issues named transactions
with support for nesting
if the name argument is set.
The transaction isolation level is not specified by DBI.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "cash", data.frame(amount = 100))
dbWriteTable(con, "account", data.frame(amount = 2000))
# All operations are carried out as logical unit:
dbBegin(con)
withdrawal <- 300
dbExecute(con, "UPDATE cash SET amount = amount + ?", list(withdrawal))
dbExecute(con, "UPDATE account SET amount = amount - ?", list(withdrawal))
dbCommit(con)
dbReadTable(con, "cash")
dbReadTable(con, "account")
# Rolling back after detecting negative value on account:
dbBegin(con)
withdrawal <- 5000
dbExecute(con, "UPDATE cash SET amount = amount + ?", list(withdrawal))
dbExecute(con, "UPDATE account SET amount = amount - ?", list(withdrawal))
if (dbReadTable(con, "account")\$amount >= 0) {
dbCommit(con)
} else {
dbRollback(con)
}
dbReadTable(con, "cash")
dbReadTable(con, "account")
dbDisconnect(con)
This section describes the behavior of the following methods:
dbWithTransaction(conn, code, ...)
dbBreak()
Given that transactions are implemented, this function
allows you to pass in code that is run in a transaction.
The default method of dbWithTransaction() calls dbBegin()
before executing the code,
and dbCommit() after successful completion,
or dbRollback() in case of an error.
The advantage is
that you don't have to remember to do dbBegin() and dbCommit() or
dbRollback() – that is all taken care of.
The special function dbBreak() allows an early exit with rollback,
it can be called only inside dbWithTransaction().
conn |
A DBIConnection object, as returned by
|
code |
An arbitrary block of R code. |
... |
Other parameters passed on to methods. |
DBI implements dbWithTransaction(), backends should need to override this
generic only if they implement specialized handling.
dbWithTransaction() returns the value of the executed code.
Failure to initiate the transaction
(e.g., if the connection is closed
or invalid
of if dbBegin() has been called already)
gives an error.
dbWithTransaction() initiates a transaction with dbBegin(), executes
the code given in the code argument, and commits the transaction with
dbCommit().
If the code raises an error, the transaction is instead aborted with
dbRollback(), and the error is propagated.
If the code calls dbBreak(), execution of the code stops and the
transaction is silently aborted.
All side effects caused by the code
(such as the creation of new variables)
propagate to the calling environment.
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "cash", data.frame(amount = 100))
dbWriteTable(con, "account", data.frame(amount = 2000))
# All operations are carried out as logical unit:
dbWithTransaction(
con,
{
withdrawal <- 300
dbExecute(con, "UPDATE cash SET amount = amount + ?", list(withdrawal))
dbExecute(con, "UPDATE account SET amount = amount - ?", list(withdrawal))
}
)
# The code is executed as if in the curent environment:
withdrawal
# The changes are committed to the database after successful execution:
dbReadTable(con, "cash")
dbReadTable(con, "account")
# Rolling back with dbBreak():
dbWithTransaction(
con,
{
withdrawal <- 5000
dbExecute(con, "UPDATE cash SET amount = amount + ?", list(withdrawal))
dbExecute(con, "UPDATE account SET amount = amount - ?", list(withdrawal))
if (dbReadTable(con, "account")\$amount < 0) {
dbBreak()
}
}
)
# These changes were not committed to the database:
dbReadTable(con, "cash")
dbReadTable(con, "account")
dbDisconnect(con)