Function qual_is_pushdown_safe

src/backend/optimizer/path/allpaths.c:4361–4448

* qual_is_pushdown_safe - is a particular rinfo safe to push down? * * rinfo is a restriction clause applying to the given subquery (whose RTE * has index rti in the parent query). * * Conditions checked here: * * 1. rinfo's clause must not contain any SubPlans (mainly because it's * unclear that it will work correctly: SubLinks will already have been * transformed into SubPlans in the qu

 * found to be unsafe to reference by subquery_is_pushdown_safe().
 */
static bool
qual_is_pushdown_safe(Query *subquery, Index rti, RestrictInfo *rinfo,
					  pushdown_safety_info *safetyInfo)
{
	bool		safe = true;
	Node	   *qual = (Node *) rinfo->clause;
	List	   *vars;
	ListCell   *vl;

	/* Refuse subselects (point 1) */
	if (contain_subplans(qual))
		return false;

	/* Refuse volatile quals if we found they'd be unsafe (point 2) */
	if (safetyInfo->unsafeVolatile &&
		contain_volatile_functions((Node *) rinfo))
		return false;

	/* Refuse leaky quals if told to (point 3) */
	if (safetyInfo->unsafeLeaky &&
		contain_leaked_vars(qual))
		return false;

	/*
	 * It would be unsafe to push down window function calls, but at least for
	 * the moment we could never see any in a qual anyhow.  (The same applies
	 * to aggregates, which we check for in pull_var_clause below.)
	 */
	Assert(!contain_window_function(qual));

	/*
	 * Examine all Vars used in clause.  Since it's a restriction clause, all
	 * such Vars must refer to subselect output columns ... unless this is
	 * part of a LATERAL subquery, in which case there could be lateral
	 * references.
	 */
	vars = pull_var_clause(qual, PVC_INCLUDE_PLACEHOLDERS);
	foreach(vl, vars)
	{
		Var		   *var = (Var *) lfirst(vl);

		/*
		 * XXX Punt if we find any PlaceHolderVars in the restriction clause.
		 * It's not clear whether a PHV could safely be pushed down, and even
		 * less clear whether such a situation could arise in any cases of
		 * practical interest anyway.  So for the moment, just refuse to push
		 * down.
		 */
		if (!IsA(var, Var))
		{
			safe = false;
			break;
		}

		/*
		 * Punt if we find any lateral references.  It would be safe to push
		 * these down, but we'd have to convert them into outer references,
		 * which subquery_push_qual lacks the infrastructure to do.  The case