Function clause_sides_match_join

src/backend/optimizer/path/joinpath.c:1239–1258

* clause_sides_match_join * Determine whether a join clause is of the right form to use in this join. * * We already know that the clause is a binary opclause referencing only the * rels in the current join. The point here is to check whether it has the * form "outerrel_expr op innerrel_expr" or "innerrel_expr op outerrel_expr", * rather than mixing outer and inner vars on either side. I

 * we set the transient flag outer_is_left to identify which side is which.
 */
static inline bool
clause_sides_match_join(RestrictInfo *rinfo, RelOptInfo *outerrel,
						RelOptInfo *innerrel)
{
	if (bms_is_subset(rinfo->left_relids, outerrel->relids) &&
		bms_is_subset(rinfo->right_relids, innerrel->relids))
	{
		/* lefthand side is outer */
		rinfo->outer_is_left = true;
		return true;
	}
	else if (bms_is_subset(rinfo->left_relids, innerrel->relids) &&
			 bms_is_subset(rinfo->right_relids, outerrel->relids))
	{
		/* righthand side is outer */
		rinfo->outer_is_left = false;
		return true;
	}
	return false;				/* no good for these input relations */
}

/*
 * sort_inner_and_outer