dbGetQueryArrow | R Documentation |
Returns the result of a query as an Arrow object.
dbGetQueryArrow()
comes with a default implementation
(which should work with most backends) that calls
dbSendQueryArrow()
, then dbFetchArrow()
, ensuring that
the result is always freed by dbClearResult()
.
For passing query parameters,
see dbSendQueryArrow()
, in particular
the "The data retrieval flow for Arrow streams" section.
For retrieving results as a data frame, see dbGetQuery()
.
dbGetQueryArrow(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 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.
However, callers are strongly advised to use
dbExecute()
for data manipulation statements.
dbGetQueryArrow()
always returns an object coercible to 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.
The object returned by dbGetQueryArrow()
can also be passed to
nanoarrow::as_nanoarrow_array_stream()
to create a nanoarrow
array stream object that can be used to read the result set
in batches.
The chunk size is implementation-specific.
The following arguments are not part of the dbGetQueryArrow()
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" and "Value" 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
For updates: dbSendStatement()
and dbExecute()
.
Other DBIConnection generics:
DBIConnection-class
,
dbAppendTable()
,
dbAppendTableArrow()
,
dbCreateTable()
,
dbCreateTableArrow()
,
dbDataType()
,
dbDisconnect()
,
dbExecute()
,
dbExistsTable()
,
dbGetException()
,
dbGetInfo()
,
dbGetQuery()
,
dbIsReadOnly()
,
dbIsValid()
,
dbListFields()
,
dbListObjects()
,
dbListResults()
,
dbListTables()
,
dbQuoteIdentifier()
,
dbReadTable()
,
dbReadTableArrow()
,
dbRemoveTable()
,
dbSendQuery()
,
dbSendQueryArrow()
,
dbSendStatement()
,
dbUnquoteIdentifier()
,
dbWriteTable()
,
dbWriteTableArrow()
Other data retrieval generics:
dbBind()
,
dbClearResult()
,
dbFetch()
,
dbFetchArrow()
,
dbFetchArrowChunk()
,
dbGetQuery()
,
dbHasCompleted()
,
dbSendQuery()
,
dbSendQueryArrow()
# Retrieve data as arrow table
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
dbGetQueryArrow(con, "SELECT * FROM mtcars")
dbDisconnect(con)
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.