Send query, retrieve results and then clear result set
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 free-d by dbClearResult().
dbGetQuery(conn, statement, ...)
conn |
A DBIConnection object, as returned by
|
statement |
a character string containing SQL. |
... |
Other parameters passed on to methods. |
This method is for SELECT queries only
(incl. other SQL statements that return a SELECT-alike result,
e. g. execution of a stored procedure).
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.
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.
Subclasses should override this method only if they provide some sort of performance optimization.
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
For updates: dbSendStatement() and dbExecute().
Other DBIConnection generics:
DBIConnection-class,
dbAppendTable(),
dbCreateTable(),
dbDataType(),
dbDisconnect(),
dbExecute(),
dbExistsTable(),
dbGetException(),
dbGetInfo(),
dbIsReadOnly(),
dbIsValid(),
dbListFields(),
dbListObjects(),
dbListResults(),
dbListTables(),
dbReadTable(),
dbRemoveTable(),
dbSendQuery(),
dbSendStatement(),
dbWriteTable()
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)
Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.