This query requests an outer join, but one or more conditions in the WHERE clause interfere with the dominant-subordinate relationships between the joined tables in the FROM clause.
Review the query, and verify that every condition that relates the joined tables is actually necessary and semantically correct.
If an expression in the WHERE clause relates two subordinate tables, you must use parentheses around the joined tables in the FROM clause to enforce dominant-subordinate relationships. (Note: You cannot put a parenthesis directly after the FROM keyword.) The following example successfully returns a result:
SELECT c.company, o.order_date, i.total_price, m.manu_name FROM customer c, OUTER (orders o, OUTER (items i, OUTER manufact m)) WHERE c.customer_num = o.customer_num AND o.order_num = i.order_num AND i.manu_code = m.manu_code;
If you omit parentheses around the subordinate tables in the FROM clause, you must establish join conditions, or relationships, between the dominant table and each subordinate table in the WHERE clause. If a join condition is between two subordinate tables, the query will fail. The following example successfully returns a result:
SELECT c.company, o.order_date, c2.call_descr FROM customer c, OUTER orders o, OUTER cust_calls c2 WHERE c.customer_num = o.customer_num AND c.customer_num = c2.customer_num;
Consider using the ANSI-SQL standard syntax for outer joins. For more information, refer to the IBM Informix Guide to SQL: Syntax.