Working with Data Models › Working with Transformations › Using the Two Table Roll Down Transformation

Using the Two Table Roll Down Transformation

You can apply a transformation to roll down two related tables and create a single table. This improves query performance and helps build a more effective physical model for a target DBMS.

Important! Once you apply the Two Table Roll Down transformation, it cannot be reversed. While in the current modeling session however, you can undo the action.

Roll-Down Denormalization Wizard

To roll down and denormalize two tables, select the identifying relationship that connects two tables and click the Two Table Roll Down icon on the Transformations toolbar.

Result of Rolling Down and Denormalizing Two Tables

When you apply a Two Table Roll Down transformation, you:

• Create a denormalized table that contains all primary key and non-key columns from the source child table and all non-key columns from the source parent table. When you create columns in the denormalized table, you preserve the column order in the source parent table, and then the column order in the source child table. The primary key of the denormalized table is the combination of primary keys from both the source parent and child tables. The denormalized table appears in the Model Explorer under the Tables folder.
• If the source child table that you denormalize contains a foreign key (FK) that does not migrate from the source parent table, you create a corresponding foreign key in the denormalized table. The foreign key in the denormalized table inherits object properties from the corresponding foreign key in the source tables.
• If the source parent or child table that you denormalize contains columns that are unified, you unify the corresponding columns in the denormalized table.
• Create all relationships associated with the source parent and child tables that you denormalize, and preserves all migrating keys.
• Preserve all object properties from the source child table.

More information:

Roll Down and Denormalize Two Tables with a Transformation