A Source Qualifier is an Active and Connected Informatica transformation that reads the rows from a relational database or flat file source.
We can configure the SQ to join [Both INNER as well as OUTER JOIN] data originating from the same source database.
We can use a source filter to reduce the number of rows the Integration Service queries.
We can specify a number for sorted ports and the Integration Service adds an ORDER BY clause to the default SQL query.
We can choose Select Distinct option for relational databases and the Integration Service adds a SELECT DISTINCT clause to the default SQL query.
Also we can write Custom/Used Defined SQL query which will override the default query in the SQ by changing the default settings of the transformation properties.
Aslo we have the option to write Pre as well as Post SQL statements to be executed before and after the SQ query in the source database.
Since the transformation provides us with the property Select Distinct , when the Integration Service adds a SELECT DISTINCT clause to the default SQL query, which in turn affects the number of rows returned by the Database to the Integration Service and hence it is an Active transformation.