Hey Shayon. IF NOT EXISTS or the Active Record version "if_not_exists: true" can be pretty handy though when there's a valid index in production, to help drive schema definition consistency in all environments (prod, dev, CI, etc.). As you pointed out though, it only makes sense when the indexes being checked are valid.

In my experience on large tables that are “busy”, sometimes indexes need to be added manually first from a utility session, perhaps inside tmux/screen that's detached from while they are created. This could take hours for large tables. Then once done, and the index is valid, an Active Record migration can be sent out using “if_not_exists: true” to make sure it’s applied everywhere.

Your point that it could be misused unintentionally due to not knowing an index is INVALID is a good one, and I feel it should be part of how it works by default in Active Record. Had you considered trying to propose that to rails/rails? I would certainly support that PR (may be able to collaborate) and could add more examples and validation.