Function MJExamineQuals

src/backend/executor/nodeMergejoin.c:189–301

* MJExamineQuals * * This deconstructs the list of mergejoinable expressions, which is given * to us by the planner in the form of a list of "leftexpr = rightexpr" * expression trees in the order matching the sort columns of the inputs. * We build an array of MergeJoinClause structs containing the information * we will need at runtime. Each struct essentially tells us how to compare * the

 *      predicate is (BoolExpr_NOT (DistinctExpr_= leftexpr rightexpr)).
 */
static MergeJoinClause
MJExamineQuals(List *mergeclauses,
			   Oid *mergefamilies,
			   Oid *mergecollations,
			   int *mergestrategies,
			   bool *mergenullsfirst,
			   PlanState *parent)
{
	MergeJoinClause clauses;
	int			nClauses = list_length(mergeclauses);
	int			iClause;
	ListCell   *cl;

	clauses = (MergeJoinClause) palloc0(nClauses * sizeof(MergeJoinClauseData));

	iClause = 0;
	foreach(cl, mergeclauses)
	{
		OpExpr	   *qual = (OpExpr *) lfirst(cl);
		MergeJoinClause clause = &clauses[iClause];
		Oid			opfamily = mergefamilies[iClause];
		Oid			collation = mergecollations[iClause];
		StrategyNumber opstrategy = mergestrategies[iClause];
		bool		nulls_first = mergenullsfirst[iClause];
		int			op_strategy;
		Oid			op_lefttype;
		Oid			op_righttype;
		Oid			sortfunc;

		if (!IsA(qual, OpExpr))
		{
			BoolExpr *bx = (BoolExpr*)qual;
			bool ok = false;
			
			if ( IsA(bx, BoolExpr) && bx->boolop == NOT_EXPR && list_length(bx->args) == 1 )
			{
				DistinctExpr *dx = (DistinctExpr*)linitial(bx->args);
				
				if ( IsA(dx, DistinctExpr) )
				{
					clause->notdistinct = true;
					qual = (OpExpr *)dx;
					ok = true;
				}
			}
			if (!ok)
				elog(ERROR, "mergejoin clause is not an OpExpr");
		}

		/*
		 * Prepare the input expressions for execution.
		 */
		clause->lexpr = ExecInitExpr((Expr *) linitial(qual->args), parent);
		clause->rexpr = ExecInitExpr((Expr *) lsecond(qual->args), parent);

		/* Set up sort support data */
		clause->ssup.ssup_cxt = CurrentMemoryContext;
		clause->ssup.ssup_collation = collation;