Function preprocess_expression

src/backend/optimizer/plan/planner.c:1404–1529

* preprocess_expression * Do subquery_planner's preprocessing work for an expression, * which can be a targetlist, a WHERE clause (including JOIN/ON * conditions), a HAVING clause, or a few other things. */

 *		conditions), a HAVING clause, or a few other things.
 */
static Node *
preprocess_expression(PlannerInfo *root, Node *expr, int kind)
{
	/*
	 * Fall out quickly if expression is empty.  This occurs often enough to
	 * be worth checking.  Note that null->null is the correct conversion for
	 * implicit-AND result format, too.
	 */
	if (expr == NULL)
		return NULL;

	/*
	 * If the query has any join RTEs, replace join alias variables with
	 * base-relation variables.  We must do this first, since any expressions
	 * we may extract from the joinaliasvars lists have not been preprocessed.
	 * For example, if we did this after sublink processing, sublinks expanded
	 * out from join aliases would not get processed.  But we can skip this in
	 * non-lateral RTE functions, VALUES lists, and TABLESAMPLE clauses, since
	 * they can't contain any Vars of the current query level.
	 */
	if (root->hasJoinRTEs &&
		!(kind == EXPRKIND_RTFUNC ||
		  kind == EXPRKIND_VALUES ||
		  kind == EXPRKIND_TABLESAMPLE ||
		  kind == EXPRKIND_TABLEFUNC))
		expr = flatten_join_alias_vars(root->parse, expr);

	if (root->parse->hasFuncsWithExecRestrictions)
	{
		if (kind == EXPRKIND_RTFUNC)
		{
			/* allowed */
		}
		else if (kind == EXPRKIND_TARGET)
		{
			/*
			 * Allowed in simple cases with no real RTEs. For example,
			 * "SELECT func()" is allowed, but "SELECT func() FROM foo" is not.
			 */
			if ((list_length(root->parse->rtable) != 1 ||
				 linitial_node(RangeTblEntry, root->parse->rtable)->rtekind != RTE_RESULT) &&
				check_execute_on_functions((Node *) root->parse->targetList) != PROEXECLOCATION_ANY)
			{
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						 errmsg("function with EXECUTE ON restrictions cannot be used in the SELECT list of a query with FROM")));
			}
		}
		else
		{
			if (check_execute_on_functions((Node *) root->parse->targetList) != PROEXECLOCATION_ANY)
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						 errmsg("function with EXECUTE ON restrictions cannot be used here")));
		}
	}

	/*