When you configure a Lookup source filter, the Integration Service performs lookups based on the results of the filter statement. For example, you might need to retrieve the last name of every employee whose ID is greater than 510.
You configure the following lookup source filter on the EmployeeID column:
EmployeeID >= 510
EmployeeID is an input port in the Lookup transformation. When the Integration Service reads the source row, it performs a lookup on the cache when the value of EmployeeID is greater than 510. When EmployeeID is less than or equal to 510, the Lookup transformation does not retrieve the last name.
When you add a lookup source filter to the Lookup query for a session configured for pushdown optimization, the Integration Service creates a view to represent the SQL override. The Integration Service runs an SQL query against this view to push the transformation logic to the database.