Function cdb_pull_up_eclass

src/backend/optimizer/path/pathkeys.c:1548–1629

* cdb_pull_up_eclass * * Given an argument EquivalenceClass, finds an EquivalenceClass whose * expr can be projected thru a given targetlist. If found, builds the * transformed key expr and returns an equivalence class containing it. * * Returns NULL if the given EC does not have any member that can be * rewritten in terms of the projected output columns. * * Note that this function doe

 * expr in determining whether an EC member expr matches a targetlist expr.
 */
EquivalenceClass *
cdb_pull_up_eclass(PlannerInfo *root,
				   EquivalenceClass *eclass,
				   Relids relids,
				   List *targetlist,
				   List *newvarlist,
				   Index newrelid,
				   bool ignore_relabel)
{
	Expr	   *sub_distkeyexpr;
	EquivalenceClass *outer_ec;
	Expr	   *newexpr = NULL;
	Index sortref = 0;
	bool	relabel_stripped = false;

	Assert(eclass);
	Assert(!newvarlist ||
		   list_length(newvarlist) == list_length(targetlist));

	/* Find an expr that we can rewrite to use the projected columns. */
	sub_distkeyexpr = cdbpullup_findEclassInTargetList(eclass, targetlist, InvalidOid, &relabel_stripped);

	/* Replace expr's Var nodes with new ones referencing the targetlist. */
	if (sub_distkeyexpr)
	{
		if (ignore_relabel && relabel_stripped)
			return eclass;

		newexpr = cdbpullup_expr(sub_distkeyexpr,
								 targetlist,
								 newvarlist,
								 newrelid);
	}
	/* If not found, see if the equiv class contains a constant expr. */
	else if (CdbEquivClassIsConstant(eclass))
	{
		ListCell   *lc;

		foreach(lc, eclass->ec_members)
		{
			EquivalenceMember *em = lfirst(lc);

			if (em->em_is_const)
			{
				newexpr = (Expr *) copyObject(em->em_expr);
				break;
			}
		}
	}
	/* Fail if no usable expr. */
	else
		return NULL;

	if (!newexpr)
		elog(ERROR, "could not pull up equivalence class using projected target list");

	/*
	 * See https://github.com/apache/cloudberry/issues/593