what is main differance between cognos sql and native sql?? which is more effcient
Cognos SQL is based off SQL 99 which is used for writing SQL that will work with any RDBMS.
Ultimately, the Cognos SQL is converted to the RDBMS specific SQL during the process by the application and client DB providers.
Cognos SQL is the SQL that is generated by the Cognos engine.
Whereas native SQL means, native to the Database (if you are using Oracle then Oracle, else SQL Server then SQL server etc).
Cognos SQL engine is a of piece proprietary technology that is jealously guarded by Cognos and very few folks in the company has access to it.
Also it depends on the connectors that you are using, i.e., between Cognos and the database. If it is ODBC there have been issues with some DB. Native connectors are always preferable less hassle.