Send query, retrieve results and then clear result set

Description

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().

Usage

dbGetQuery(conn, statement, ...)

Arguments

Details

This method is for SELECT queries only. 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.

Value

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.

Implementation notes

Subclasses should override this method only if they provide some sort of performance optimization.

Specification

Fetching multi-row queries with one or more columns be default 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, the result is returned in full without warning. 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.

A column named row_names is treated like any other column.

See Also

For updates: dbSendStatement() and dbExecute().

Other DBIConnection generics: DBIConnection-class, dbDataType, dbDisconnect, dbExecute, dbExistsTable, dbGetException, dbGetInfo, dbIsValid, dbListFields, dbListResults, dbListTables, dbReadTable, dbRemoveTable, dbSendQuery, dbSendStatement, dbWriteTable

Examples

con <- dbConnect(RSQLite::SQLite(), ":memory:")

dbWriteTable(con, "mtcars", mtcars)
dbGetQuery(con, "SELECT * FROM mtcars")

dbDisconnect(con)