Function sort_inner_and_outer

src/backend/optimizer/path/joinpath.c:1271–1462

* sort_inner_and_outer * Create mergejoin join paths by explicitly sorting both the outer and * inner join relations on each available merge ordering. * * 'joinrel' is the join relation * 'outerrel' is the outer join relation * 'innerrel' is the inner join relation * 'jointype' is the type of join to do * 'extra' contains additional input values */

 * 'extra' contains additional input values
 */
static void
sort_inner_and_outer(PlannerInfo *root,
					 RelOptInfo *joinrel,
					 RelOptInfo *outerrel,
					 RelOptInfo *innerrel,
					 JoinType jointype,
					 JoinPathExtraData *extra)
{
	JoinType	save_jointype = jointype;
	Path	   *outer_path;
	Path	   *inner_path;
	Path	   *cheapest_partial_outer = NULL;
	Path	   *cheapest_safe_inner = NULL;
	List	   *all_pathkeys;
	ListCell   *l;

	if (jointype == JOIN_DEDUP_SEMI || jointype == JOIN_DEDUP_SEMI_REVERSE)
		jointype = JOIN_INNER;

	/*
	 * We only consider the cheapest-total-cost input paths, since we are
	 * assuming here that a sort is required.  We will consider
	 * cheapest-startup-cost input paths later, and only if they don't need a
	 * sort.
	 *
	 * This function intentionally does not consider parameterized input
	 * paths, except when the cheapest-total is parameterized.  If we did so,
	 * we'd have a combinatorial explosion of mergejoin paths of dubious
	 * value.  This interacts with decisions elsewhere that also discriminate
	 * against mergejoins with parameterized inputs; see comments in
	 * src/backend/optimizer/README.
	 */
	outer_path = outerrel->cheapest_total_path;
	inner_path = innerrel->cheapest_total_path;

	/*
	 * If either cheapest-total path is parameterized by the other rel, we
	 * can't use a mergejoin.  (There's no use looking for alternative input
	 * paths, since these should already be the least-parameterized available
	 * paths.)
	 */
	if (PATH_PARAM_BY_REL(outer_path, innerrel) ||
		PATH_PARAM_BY_REL(inner_path, outerrel))
		return;

	/*
	 * If unique-ification is requested, do it and then handle as a plain
	 * inner join.
	 */
	if (jointype == JOIN_UNIQUE_OUTER)
	{
		outer_path = (Path *) create_unique_path(root, outerrel,
												 outer_path, extra->sjinfo);
		Assert(outer_path);
		jointype = JOIN_INNER;
	}
	else if (jointype == JOIN_UNIQUE_INNER)
	{