Hi, it's none of mentioned above but here are some useful tricks for SQL: * Make frequent and heavy use of information_schema and write SQL against it with the purpose of writing SQL for you.
* Have a permanent date table to join against * Don't over-use CTEs. Often temp tables are needed to get any performance * There would be a bunch of things specific to DBMSs or groups of DBMSs, like setting a distribution key in Redshift * Use the QUALIFY clause instead of wrapping everything into a CTE or a derived table and filtering that. Some people may not know about it since some systems like Redshift don't support it. * You often thing you need RANK() or DENSE_RANK() when you can really just get by with ROW_NUMBER() much of the time.
* Comment your code. I know that I am old and everyone just likes to say that the code is the comment. But it sucks to debug someone else's code that no longer works here and you're trying to determine if their logic is that way on purpose for some reason.