Can custom/manually built projections degrade Query performance

Sure they can! But are your queries using the created projections? Check with the EXPLAIN command. There is also a PROJECTION_USAGE system table that you can query to see what projections are being used.

Thanks for your reply ...we are building it test environment. Projections were built assuming some of the customer use csses . These newly built projectuons are used .but not sure on production environment, if they will be picked . Therfore wanted to check ; can we say wrongly designed peojectiin can cause degrade in performance. Can wrongly designed projection cause hash joins over merge joins ? What is check list or criTeria to state if The projection is good or bad? ..if its just case of noT be used , we are ok ..if it causes Performances degrade that is what i want to avioD