SQL override in Source qualifier and look ups in Informatica
SQL override is commonly used by ETL developers in Source qualifiers and Lookup transformation. To override SQL in source qualifier you can generate the SQL from the properties tab of the source qualifier and do all the necessary modifications to the SQL. All you have to keep in mind is the columns in the select statement match the order of the ports in the source qualifier. The ports have to be mapped to the transformation next to the source qualifier. The diagram below shows a simple SQL override. Similarly SQLs can be override in the lookups too.
The advantages of SQL override in Informatica:
a) You can put a lot of logic in the SQL override. The SQL will be executed in the source database and the results will be pulled in by the Informatica powercenter. Instead of reading all the records from the table, by writing SQL override you can filter, aggregate, etc on the source database and pull in the result set.
b) Similarly in the Lookups instead of reading all the columns from a table, you can read only the required columns from the table by doing SQL override and removing all the unnecessary ports. Also you can aggregate , filter, etc on the records that needs to be read.
c) If you are comfortable with SQL you would prefer this path instead of implementing a lot of stuff that can be achieved with SQLs.