Function exec_stmt_fetch

src/pl/plpgsql/src/pl_exec.c:4757–4842

---------- * exec_stmt_fetch Fetch from a cursor into a target, or just * move the current position of the cursor * ---------- */

 * ----------
 */
static int
exec_stmt_fetch(PLpgSQL_execstate *estate, PLpgSQL_stmt_fetch *stmt)
{
	PLpgSQL_var *curvar;
	long		how_many = stmt->how_many;
	SPITupleTable *tuptab;
	Portal		portal;
	char	   *curname;
	uint64		n;
	MemoryContext oldcontext;

	/* ----------
	 * Get the portal of the cursor by name
	 * ----------
	 */
	curvar = (PLpgSQL_var *) (estate->datums[stmt->curvar]);
	if (curvar->isnull)
		ereport(ERROR,
				(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
				 errmsg("cursor variable \"%s\" is null", curvar->refname)));

	/* Use eval_mcontext for short-lived string */
	oldcontext = MemoryContextSwitchTo(get_eval_mcontext(estate));
	curname = TextDatumGetCString(curvar->value);
	MemoryContextSwitchTo(oldcontext);

	portal = SPI_cursor_find(curname);
	if (portal == NULL)
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_CURSOR),
				 errmsg("cursor \"%s\" does not exist", curname)));

	/* Calculate position for FETCH_RELATIVE or FETCH_ABSOLUTE */
	if (stmt->expr)
	{
		bool		isnull;

		/* XXX should be doing this in LONG not INT width */
		how_many = exec_eval_integer(estate, stmt->expr, &isnull);

		if (isnull)
			ereport(ERROR,
					(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
					 errmsg("relative or absolute cursor position is null")));

		exec_eval_cleanup(estate);
	}

	if (!stmt->is_move)
	{
		PLpgSQL_variable *target;

		/* ----------
		 * Fetch 1 tuple from the cursor
		 * ----------
		 */
		SPI_scroll_cursor_fetch(portal, stmt->direction, how_many);
		tuptab = SPI_tuptable;