Source Qualifier Query is not working when I run the workflow?

Check the below things when you counter error in a Source Qualifier :

•  Always validate the source query before saving it and running the session.There may be  syntax  error.
•  Check that the database login in both source qualifier and the corresponding  session are the same.
•  Test the SQL query in some client tools like SQL developer and confirm that the data is correct
•  Check that all joins are proper in the Source Qualifier
•  Also make sure that all the ports in select list from the Source Qualifier is taken into the next level
•  The order in which the cols are given in Source Qualifier query should be in same order   as its in the Ports tab
•  Review the session log file if you need further information.