A custom query overrides the default SQL query that the Data Integration Service uses to read data from a relational source. The custom query also overrides the simple query settings that you define when you enter a source filter, use sorted ports, enter a user-defined join, or select distinct ports.

You can create a custom query to perform SQL operations that are valid in the database language but not available in the transformation language. When you define a custom query in a customized data object, you can reuse the object in multiple mappings or profiles.

Use the following guidelines when you create a custom query in a customized data object:

If you use a customized data object to perform a self-join, you must enter a custom SQL query that includes the self-join. You can use a customized data object with a custom query as a source in a mapping. The source database executes the query before it passes data to the Data Integration Service. You can create a custom query to add sources to an empty customized data object. You can also use a custom query to override the default SQL query.