When you add a relational or a flat file source definition to a mapping, you need to connect it to a Source Qualifier transformation. The Source Qualifier transformation represents the rows that the Integration Service reads when it runs a session. The Source Qualifier transformation is an active transformation.
Use the Source Qualifier transformation to complete the following tasks:
Join data originating from the same source database.
You can join two or more tables with primary key-foreign key relationships by linking the sources to one Source Qualifier transformation.
Filter rows when the Integration Service reads source data.
If you include a filter condition, the Integration Service adds a WHERE clause to the default query.
Specify an outer join rather than the default inner join.
If you include a user-defined join, the Integration Service replaces the join information specified by the metadata in the SQL query.
Specify sorted ports.
If you specify a number for sorted ports, the Integration Service adds an ORDER BY clause to the default SQL query.
Select only distinct values from the source.
If you choose Select Distinct, the Integration Service adds a SELECT DISTINCT statement to the default SQL query.
Create a custom query to issue a special SELECT statement for the Integration Service to read source data.
For example, you might use a custom query to perform aggregate calculations.