Function ExecResult

src/backend/executor/nodeResult.c:76–171

---------------------------------------------------------------- * ExecResult(node) * * returns the tuples from the outer plan which satisfy the * qualification clause. Since result nodes with right * subtrees are never planned, we ignore the right subtree * entirely (for now).. -cim 10/7/89 * * The qualification containing only constant clauses are * checked first before any proc

 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecResult(PlanState *pstate)
{
	ResultState *node = castNode(ResultState, pstate);
	TupleTableSlot *outerTupleSlot;
	PlanState  *outerPlan;
	ExprContext *econtext;

	CHECK_FOR_INTERRUPTS();

	econtext = node->ps.ps_ExprContext;

	/*
	 * check constant qualifications like (2 > 1), if not already done
	 */
	if (node->rs_checkqual)
	{
		bool		qualResult = ExecQual(node->resconstantqual, econtext);

		node->rs_checkqual = false;
		if (!qualResult)
		{
			node->rs_done = true;
			return NULL;
		}
	}

	/*
	 * Reset per-tuple memory context to free any expression evaluation
	 * storage allocated in the previous tuple cycle.
	 */
	ResetExprContext(econtext);

	/*
	 * if rs_done is true then it means that we were asked to return a
	 * constant tuple and we already did the last time ExecResult() was
	 * called, OR that we failed the constant qual check. Either way, now we
	 * are through.
	 */
	while (!node->rs_done)
	{
		outerPlan = outerPlanState(node);

		if (outerPlan != NULL)
		{
			/*
			 * retrieve tuples from the outer plan until there are no more.
			 */
			outerTupleSlot = ExecProcNode(outerPlan);

			if (TupIsNull(outerTupleSlot))
				return NULL;

			/*
			 * prepare to compute projection expressions, which will expect to
			 * access the input tuples as varno OUTER.
			 */
			econtext->ecxt_outertuple = outerTupleSlot;