SPI_cursor_open
SPI_cursor_open — set up a cursor using a statement created with SPI_prepare
Synopsis
Portal SPI_cursor_open(const char *name
, SPIPlanPtrplan
, Datum *values
, const char *nulls
, boolread_only
)
Description
SPI_cursor_open
sets up a cursor (internally, a portal) that will execute a statement prepared by SPI_prepare
. The parameters have the same meanings as the corresponding parameters to SPI_execute_plan
.
Using a cursor instead of executing the statement directly has two benefits. First, the result rows can be retrieved a few at a time, avoiding memory overrun for queries that return many rows. Second, a portal can outlive the current C function (it can, in fact, live to the end of the current transaction). Returning the portal name to the C function's caller provides a way of returning a row set as result.
The passed-in parameter data will be copied into the cursor's portal, so it can be freed while the cursor still exists.
Arguments
const char *
name
name for portal, or
NULL
to let the system select a nameSPIPlanPtr
plan
prepared statement (returned by
SPI_prepare
)Datum *
values
An array of actual parameter values. Must have same length as the statement's number of arguments.
const char *
nulls
An array describing which parameters are null. Must have same length as the statement's number of arguments.
If
nulls
isNULL
thenSPI_cursor_open
assumes that no parameters are null. Otherwise, each entry of thenulls
array should be' '
if the corresponding parameter value is non-null, or'n'
if the corresponding parameter value is null. (In the latter case, the actual value in the correspondingvalues
entry doesn't matter.) Note thatnulls
is not a text string, just an array: it does not need a'\0'
terminator.bool
read_only
true
for read-only execution
Return Value
Pointer to portal containing the cursor. Note there is no error return convention; any error will be reported via elog
.