# 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, SPIPlanPtr plan,
Datum * values, const char * nulls,
bool read_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 name
SPIPlanPtr *
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
is NULL
then SPI_cursor_open
assumes that no parameters are null. Otherwise, each entry of the nulls
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 corresponding values
entry doesn't matter.) Note that nulls
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
.