initsplan.c

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	ojinfo->min_righthand = min_righthand;

	return ojinfo;
}


/*****************************************************************************
 *
 *	  QUALIFICATIONS
 *
 *****************************************************************************/

/*
 * distribute_qual_to_rels
 *	  Add clause information to either the baserestrictinfo or joininfo list
 *	  (depending on whether the clause is a join) of each base relation
 *	  mentioned in the clause.	A RestrictInfo node is created and added to
 *	  the appropriate list for each rel.  Alternatively, if the clause uses a
 *	  mergejoinable operator and is not delayed by outer-join rules, enter
 *	  the left- and right-side expressions into the query's list of
 *	  EquivalenceClasses.
 *
 * 'clause': the qual clause to be distributed
 * 'is_deduced': TRUE if the qual came from implied-equality deduction
 * 'below_outer_join': TRUE if the qual is from a JOIN/ON that is below the
 *		nullable side of a higher-level outer join
 * 'qualscope': set of baserels the qual's syntactic scope covers
 * 'ojscope': NULL if not an outer-join qual, else the minimum set of baserels
 *		needed to form this join
 * 'outerjoin_nonnullable': NULL if not an outer-join qual, else the set of
 *		baserels appearing on the outer (nonnullable) side of the join
 *		(for FULL JOIN this includes both sides of the join, and must in fact
 *		equal qualscope)
 *
 * 'qualscope' identifies what level of JOIN the qual came from syntactically.
 * 'ojscope' is needed if we decide to force the qual up to the outer-join
 * level, which will be ojscope not necessarily qualscope.
 */
static void
distribute_qual_to_rels(PlannerInfo *root, Node *clause,
						bool is_deduced,
						bool below_outer_join,
						Relids qualscope,
						Relids ojscope,
						Relids outerjoin_nonnullable)
{
	Relids		relids;
	bool		is_pushed_down;
	bool		outerjoin_delayed;
	bool		pseudoconstant = false;
	bool		maybe_equivalence;
	bool		maybe_outer_join;
	RestrictInfo *restrictinfo;

	/*
	 * Retrieve all relids mentioned within the clause.
	 */
	relids = pull_varnos(clause);

	/*
	 * Cross-check: clause should contain no relids not within its scope.
	 * Otherwise the parser messed up.
	 */
	if (!bms_is_subset(relids, qualscope))
		elog(ERROR, "JOIN qualification cannot refer to other relations");
	if (ojscope && !bms_is_subset(relids, ojscope))
		elog(ERROR, "JOIN qualification cannot refer to other relations");

	/*
	 * If the clause is variable-free, our normal heuristic for pushing it
	 * down to just the mentioned rels doesn't work, because there are none.
	 *
	 * If the clause is an outer-join clause, we must force it to the OJ's
	 * semantic level to preserve semantics.
	 *
	 * Otherwise, when the clause contains volatile functions, we force it to
	 * be evaluated at its original syntactic level.  This preserves the
	 * expected semantics.
	 *
	 * When the clause contains no volatile functions either, it is actually a
	 * pseudoconstant clause that will not change value during any one
	 * execution of the plan, and hence can be used as a one-time qual in a
	 * gating Result plan node.  We put such a clause into the regular
	 * RestrictInfo lists for the moment, but eventually createplan.c will
	 * pull it out and make a gating Result node immediately above whatever
	 * plan node the pseudoconstant clause is assigned to.	It's usually best
	 * to put a gating node as high in the plan tree as possible. If we are
	 * not below an outer join, we can actually push the pseudoconstant qual
	 * all the way to the top of the tree.	If we are below an outer join, we
	 * leave the qual at its original syntactic level (we could push it up to
	 * just below the outer join, but that seems more complex than it's
	 * worth).
	 */
	if (bms_is_empty(relids))
	{
		if (ojscope)
		{
			/* clause is attached to outer join, eval it there */
			relids = bms_copy(ojscope);
			/* mustn't use as gating qual, so don't mark pseudoconstant */
		}
		else
		{
			/* eval at original syntactic level */
			relids = bms_copy(qualscope);
			if (!contain_volatile_functions(clause))
			{
				/* mark as gating qual */
				pseudoconstant = true;
				/* tell createplan.c to check for gating quals */
				root->hasPseudoConstantQuals = true;
				/* if not below outer join, push it to top of tree */
				if (!below_outer_join)
					relids = get_relids_in_jointree((Node *) root->parse->jointree);
			}
		}
	}

	/*----------
	 * Check to see if clause application must be delayed by outer-join
	 * considerations.
	 *
	 * A word about is_pushed_down: we mark the qual as "pushed down" if
	 * it is (potentially) applicable at a level different from its original
	 * syntactic level.  This flag is used to distinguish OUTER JOIN ON quals
	 * from other quals pushed down to the same joinrel.  The rules are:
	 *		WHERE quals and INNER JOIN quals: is_pushed_down = true.
	 *		Non-degenerate OUTER JOIN quals: is_pushed_down = false.
	 *		Degenerate OUTER JOIN quals: is_pushed_down = true.
	 * A "degenerate" OUTER JOIN qual is one that doesn't mention the
	 * non-nullable side, and hence can be pushed down into the nullable side
	 * without changing the join result.  It is correct to treat it as a
	 * regular filter condition at the level where it is evaluated.
	 *
	 * Note: it is not immediately obvious that a simple boolean is enough
	 * for this: if for some reason we were to attach a degenerate qual to
	 * its original join level, it would need to be treated as an outer join
	 * qual there.	However, this cannot happen, because all the rels the
	 * clause mentions must be in the outer join's min_righthand, therefore
	 * the join it needs must be formed before the outer join; and we always
	 * attach quals to the lowest level where they can be evaluated.  But
	 * if we were ever to re-introduce a mechanism for delaying evaluation
	 * of "expensive" quals, this area would need work.
	 *----------
	 */
	if (is_deduced)
	{
		/*
		 * If the qual came from implied-equality deduction, it should not be
		 * outerjoin-delayed, else deducer blew it.  But we can't check this
		 * because the ojinfo list may now contain OJs above where the qual
		 * belongs.
		 */
		Assert(!ojscope);
		is_pushed_down = true;
		outerjoin_delayed = false;
		/* Don't feed it back for more deductions */
		maybe_equivalence = false;
		maybe_outer_join = false;
	}
	else if (bms_overlap(relids, outerjoin_nonnullable))
	{
		/*
		 * The qual is attached to an outer join and mentions (some of the)
		 * rels on the nonnullable side, so it's not degenerate.
		 *
		 * We can't use such a clause to deduce equivalence (the left and
		 * right sides might be unequal above the join because one of them has
		 * gone to NULL) ... but we might be able to use it for more limited
		 * deductions, if it is mergejoinable.  So consider adding it to the
		 * lists of set-aside outer-join clauses.
		 */
		is_pushed_down = false;
		maybe_equivalence = false;
		maybe_outer_join = true;

		/* Check to see if must be delayed by lower outer join */
		outerjoin_delayed = check_outerjoin_delay(root, &relids, false);

		/*
		 * Now force the qual to be evaluated exactly at the level of joining
		 * corresponding to the outer join.  We cannot let it get pushed down
		 * into the nonnullable side, since then we'd produce no output rows,
		 * rather than the intended single null-extended row, for any
		 * nonnullable-side rows failing the qual.
		 *
		 * (Do this step after calling check_outerjoin_delay, because that
		 * trashes relids.)
		 */
		Assert(ojscope);
		relids = ojscope;
		Assert(!pseudoconstant);
	}
	else
	{
		/*
		 * Normal qual clause or degenerate outer-join clause.	Either way, we
		 * can mark it as pushed-down.
		 */
		is_pushed_down = true;

		/* Check to see if must be delayed by lower outer join */
		outerjoin_delayed = check_outerjoin_delay(root, &relids, true);

		if (outerjoin_delayed)
		{
			/* Should still be a subset of current scope ... */
			Assert(bms_is_subset(relids, qualscope));

			/*
			 * Because application of the qual will be delayed by outer join,
			 * we mustn't assume its vars are equal everywhere.
			 */
			maybe_equivalence = false;
		}
		else
		{
			/*
			 * Qual is not delayed by any lower outer-join restriction, so we
			 * can consider feeding it to the equivalence machinery. However,
			 * if it's itself within an outer-join clause, treat it as though
			 * it appeared below that outer join (note that we can only get
			 * here when the clause references only nullable-side rels).
			 */
			maybe_equivalence = true;
			if (outerjoin_nonnullable != NULL)
				below_outer_join = true;
		}

		/*
		 * Since it doesn't mention the LHS, it's certainly not useful as a
		 * set-aside OJ clause, even if it's in an OJ.
		 */
		maybe_outer_join = false;
	}

	/*
	 * Build the RestrictInfo node itself.
	 */
	restrictinfo = make_restrictinfo((Expr *) clause,
									 is_pushed_down,
									 outerjoin_delayed,
									 pseudoconstant,
									 relids);

	/*
	 * If it's a join clause (either naturally, or because delayed by
	 * outer-join rules), add vars used in the clause to targetlists of their
	 * relations, so that they will be emitted by the plan nodes that scan
	 * those relations (else they won't be available at the join node!).
	 *
	 * Note: if the clause gets absorbed into an EquivalenceClass then this
	 * may be unnecessary, but for now we have to do it to cover the case
	 * where the EC becomes ec_broken and we end up reinserting the original
	 * clauses into the plan.
	 */
	if (bms_membership(relids) == BMS_MULTIPLE)
	{
		List	   *vars = pull_var_clause(clause, false);

		add_vars_to_targetlist(root, vars, relids);
		list_free(vars);
	}

	/*
	 * We check "mergejoinability" of every clause, not only join clauses,
	 * because we want to know about equivalences between vars of the same
	 * relation, or between vars and consts.
	 */
	check_mergejoinable(restrictinfo);

	/*
	 * If it is a true equivalence clause, send it to the EquivalenceClass
	 * machinery.  We do *not* attach it directly to any restriction or join
	 * lists.  The EC code will propagate it to the appropriate places later.
	 *
	 * If the clause has a mergejoinable operator and is not
	 * outerjoin-delayed, yet isn't an equivalence because it is an outer-join
	 * clause, the EC code may yet be able to do something with it.  We add it
	 * to appropriate lists for further consideration later.  Specifically:
	 *
	 * If it is a left or right outer-join qualification that relates the two
	 * sides of the outer join (no funny business like leftvar1 = leftvar2 +
	 * rightvar), we add it to root->left_join_clauses or
	 * root->right_join_clauses according to which side the nonnullable
	 * variable appears on.
	 *
	 * If it is a full outer-join qualification, we add it to
	 * root->full_join_clauses.  (Ideally we'd discard cases that aren't
	 * leftvar = rightvar, as we do for left/right joins, but this routine
	 * doesn't have the info needed to do that; and the current usage of the
	 * full_join_clauses list doesn't require that, so it's not currently
	 * worth complicating this routine's API to make it possible.)
	 *
	 * If none of the above hold, pass it off to
	 * distribute_restrictinfo_to_rels().
	 */
	if (restrictinfo->mergeopfamilies)
	{
		if (maybe_equivalence)
		{
			if (process_equivalence(root, restrictinfo, below_outer_join))
				return;
			/* EC rejected it, so pass to distribute_restrictinfo_to_rels */
		}
		else if (maybe_outer_join && restrictinfo->can_join)
		{
			if (bms_is_subset(restrictinfo->left_relids,
							  outerjoin_nonnullable) &&
				!bms_overlap(restrictinfo->right_relids,
							 outerjoin_nonnullable))
			{
				/* we have outervar = innervar */
				root->left_join_clauses = lappend(root->left_join_clauses,
												  restrictinfo);
				return;
			}
			if (bms_is_subset(restrictinfo->right_relids,
							  outerjoin_nonnullable) &&
				!bms_overlap(restrictinfo->left_relids,
							 outerjoin_nonnullable))
			{
				/* we have innervar = outervar */
				root->right_join_clauses = lappend(root->right_join_clauses,
												   restrictinfo);
				return;
			}
			if (bms_equal(outerjoin_nonnullable, qualscope))
			{
				/* FULL JOIN (above tests cannot match in this case) */
				root->full_join_clauses = lappend(root->full_join_clauses,
												  restrictinfo);
				return;
			}
		}
	}

	/* No EC special case applies, so push it into the clause lists */
	distribute_restrictinfo_to_rels(root, restrictinfo);
}