When you add a user-defined join to a customized data object or a relational data object instance, you can use the data object as a read transformation in a mapping. The source database performs the join before it passes data to the Data Integration Service. Mapping performance increases when the source tables are indexed.

Creat a user-defined join to join data from related sources. The user-defined join overrides the default inner join that the Data Integration creates based on the related keys in each source. When you enter a user-defined join, enter the contents of the WHERE clause that specifies the join condition. If the user-defined join performs an outer join, the Data Integration Service might insert the join syntax in the WHERE clause or the FROM clause, based on the database syntax.

You might need to enter a user-defined join in the following circumstances:

Use the following guidelines when you enter a user-defined join in a customized data object or relational data object instance:

User-defined joins join data from related resources in a database. To join heterogeneous sources, use a Joiner transformation in a mapping that reads data from the sources. To perform a self-join, you must enter a custom SQL query that includes the self-join.