SQL Awesomeness: Finding a QUALIFY query clause in the depths of the database ocean
After so many years of writing SQL queries, I cannot believe I never came across a QUALIFY query clause. It feels like discovering a treasure in the depths of the database ocean. Even ChatGPT was not aware of it! QUALIFY query clause was invented by Teradata and is not a part of SQL Standart but apparently, multiple database vendors are supporting it, for instance, Snowflake and Databricks. QUALIFY clause solves the challenge when applying a window function as a query filter. SQL Standart and most database vendors will not allow to run of a window function as a part of a WHERE clause because window functions get evaluated after the HAVING clause. We typically create a CTE or subquery adding a window function to be able to filter on a it at a later query stage. Here is an example of how you can use QUALIFY to piece-of-cake filter on the window function. I will use the Snowflake database, as an example. Let us consider that we have a list of queries and we need to find the last quer...