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.