Sybase SQL Server 4.9.2 and Microsoft SQL Server 4.2x subqueries are not SQL-92 standard; subqueries can return duplicate rows.
Sybase System 10 defaults to SQL-92 standard behavior, but the old subquery behavior can be turned on to ease migration. Sybase 10 is backward compatible to the non-ANSI behavior if the SET DUP_IN_SUBQUERY option is turned ON. Sybase 11 and Microsoft SQL Server 7.0 support only SQL-92 subquery behavior. If you are migrating an application from Sybase 10 and the system uses SET DUP_IN_SUBQUERY ON, you must review the Sybase queries so that they do not cause errors. If you are migrating from a Sybase version previous to 10, you also must review queries that have subqueries.