Function ExecReScanSetOp

src/backend/executor/nodeSetOp.c:597–651

void
ExecReScanSetOp(SetOpState *node)
{
	ExecClearTuple(node->ps.ps_ResultTupleSlot);
	node->setop_done = false;
	node->numOutput = 0;

	if (((SetOp *) node->ps.plan)->strategy == SETOP_HASHED)
	{
		/*
		 * In the hashed case, if we haven't yet built the hash table then we
		 * can just return; nothing done yet, so nothing to undo. If subnode's
		 * chgParam is not NULL then it will be re-scanned by ExecProcNode,
		 * else no reason to re-scan it at all.
		 */
		if (!node->table_filled)
			return;

		/*
		 * If we do have the hash table and the subplan does not have any
		 * parameter changes, then we can just rescan the existing hash table;
		 * no need to build it again.
		 */
		if (node->ps.lefttree->chgParam == NULL)
		{
			ResetTupleHashIterator(node->hashtable, &node->hashiter);
			return;
		}
	}

	/* Release first tuple of group, if we have made a copy */
	if (node->grp_firstTuple != NULL)
	{
		heap_freetuple(node->grp_firstTuple);
		node->grp_firstTuple = NULL;
	}

	/* Release any hashtable storage */
	if (node->tableContext)
		MemoryContextResetAndDeleteChildren(node->tableContext);

	/* And rebuild empty hashtable if needed */
	if (((SetOp *) node->ps.plan)->strategy == SETOP_HASHED)
	{
		ResetTupleHashTable(node->hashtable);
		node->table_filled = false;
	}

	/*
	 * if chgParam of subnode is not null then plan will be re-scanned by
	 * first ExecProcNode.
	 */
	if (node->ps.lefttree->chgParam == NULL)
		ExecReScan(node->ps.lefttree);
}