Function setop_fill_hash_table

src/backend/executor/nodeSetOp.c:338–419

* ExecSetOp for hashed case: phase 1, read input and build hash table */

 * ExecSetOp for hashed case: phase 1, read input and build hash table
 */
static void
setop_fill_hash_table(SetOpState *setopstate)
{
	SetOp	   *node = (SetOp *) setopstate->ps.plan;
	PlanState  *outerPlan;
	int			firstFlag;
	bool		in_first_rel PG_USED_FOR_ASSERTS_ONLY;
	ExprContext *econtext = setopstate->ps.ps_ExprContext;

	/*
	 * get state info from node
	 */
	outerPlan = outerPlanState(setopstate);
	firstFlag = node->firstFlag;
	/* verify planner didn't mess up */
	Assert(firstFlag == 0 ||
		   (firstFlag == 1 &&
			(node->cmd == SETOPCMD_INTERSECT ||
			 node->cmd == SETOPCMD_INTERSECT_ALL)));

	/*
	 * Process each outer-plan tuple, and then fetch the next one, until we
	 * exhaust the outer plan.
	 */
	in_first_rel = true;
	for (;;)
	{
		TupleTableSlot *outerslot;
		int			flag;
		TupleHashEntryData *entry;
		bool		isnew;

		outerslot = ExecProcNode(outerPlan);
		if (TupIsNull(outerslot))
			break;

		/* Identify whether it's left or right input */
		flag = fetch_tuple_flag(setopstate, outerslot);

		if (flag == firstFlag)
		{
			/* (still) in first input relation */
			Assert(in_first_rel);

			/* Find or build hashtable entry for this tuple's group */
			entry = LookupTupleHashEntry(setopstate->hashtable, outerslot,
										 &isnew, NULL);

			/* If new tuple group, initialize counts */
			if (isnew)
			{
				entry->additional = (SetOpStatePerGroup)
					MemoryContextAlloc(setopstate->hashtable->tablecxt,
									   sizeof(SetOpStatePerGroupData));
				initialize_counts((SetOpStatePerGroup) entry->additional);
			}

			/* Advance the counts */