When you add a WHERE clause in a Lookup transformation using a dynamic cache, connect a Filter transformation before the Lookup transformation to filter rows that you do not want to insert into the cache or target table. If you do not include the Filter transformation, you might get inconsistent results between the cache and the target table.
For example, you configure a Lookup transformation to perform a dynamic lookup on the employee table, EMP, matching rows by EMP_ID. You define the following lookup SQL override:
SELECT EMP_ID, EMP_STATUS FROM EMP ORDER BY EMP_ID, EMP_STATUS WHERE EMP_STATUS = 4
When you first run the
, the Integration Service builds the lookup cache from the target table based on the lookup SQL override. All rows in the cache match the condition in the WHERE clause,
EMP_STATUS = 4
For example, the Integration Service reads a source row that meets the lookup condition you specify, but the value of EMP_STATUS is 2. Although the target might have the row where EMP_STATUS is 2, the Integration Service does not find the row in the cache because of the SQL override. The Integration Service inserts the row into the cache and passes the row to the target table. When the Integration Service inserts this row in the target table, you might get inconsistent results when the row already exists. In addition, not all rows in the cache match the condition in the WHERE clause in the SQL override.
To verify that you only insert rows into the cache that match the WHERE clause, add a Filter transformation before the Lookup transformation and define the filter condition as the condition in the WHERE clause in the lookup SQL override.
For the example above, enter the following filter condition in the Filter transformation and the WHERE clause in the SQL override:
EMP_STATUS = 4