Methods and apparatus, including computer program products, implementing and using techniques for executing a query in a computer to retrieve data from a relational database stored on a data storage device. A query is received that contains a CASE expression having one or more subqueries. A query execution plan is generated. The query execution plan uses a parameterized union all operator to keep the semantics of the CASE expression, and a nested loop join operator to drive data across the section of the query execution plan that executes the CASE expression without performing any join operations. The generated query execution plan is executed in the computer to retrieve data from the relational database.