That is quite a hyperbolic statement and I have to disagree with you. I've used SQL on a variety of databases over 15 years, and yes while some like MySQL have poorly implemented anything other than basic SQL/RDBMS features, most are very similar in feature sets. There are vendors-specific additional features like how Oracle supports hierarchical queries with CONNECT, but you don't have to use them.

- CTEs are very close if not the same across Oracle, PostgreSQL, DB2, Hive, Snowflake, and MS SQL Server - I believe even Sybase too but it's been a while. - Joins work all largely the same even though a couple of those support additional join types, especially when you want to join on functions that return data sets. - Window functions are supported by every major DB with similar or the same syntax too. Any differences take 5sec to lookup in documentation.

My only complaint is loading data is highly vendor specific.