You can push transformation logic to the source or target database using pushdown optimization. When you run a session configured for pushdown optimization, the Integration Service translates the transformation logic into SQL queries and sends the SQL queries to the database. The source or target database executes the SQL queries to process the transformations.
The amount of transformation logic you can push to the database depends on the database, transformation logic, and mapping and session configuration. The Integration Service processes all transformation logic that it cannot push to a database.
Use the Pushdown Optimization Viewer to preview the SQL statements and mapping logic that the Integration Service can push to the source or target database. You can also use the Pushdown Optimization Viewer to view the messages related to pushdown optimization.
The following figure shows a mapping containing transformation logic that can be pushed to the source database:
This mapping contains an Expression transformation that creates an item ID based on the store number 5419 and the item ID from the source. To push the transformation logic to the database, the Integration Service generates the following SQL statement:
INSERT INTO T_ITEMS(ITEM_ID, ITEM_NAME, ITEM_DESC) SELECT CAST((CASE WHEN 5419 IS NULL THEN '' ELSE 5419 END) + '_' + (CASE WHEN ITEMS.ITEM_ID IS NULL THEN '' ELSE ITEMS.ITEM_ID END) AS INTEGER), ITEMS.ITEM_NAME, ITEMS.ITEM_DESC FROM ITEMS2 ITEMS
The Integration Service generates an INSERT SELECT statement to retrieve the ID, name, and description values from the source table, create new item IDs, and insert the values into the ITEM_ID, ITEM_NAME, and ITEM_DESC columns in the target table. It concatenates the store number 5419, an underscore, and the original ITEM ID to get the new item ID.