SQL is a standard with approximately zero fully-compliant implementations. What's more, every database has a variety of features that aren't covered by the SQL

SQL is a standard with approximately zero fully-compliant implementations. What's more, every database has a variety of features that aren't covered by the SQL spec, or use different syntax for some feature for historical reasons. I've got a lot of respect for the PostgreSQL devs for occasionally breaking backwards-compatibility in the name of ANSI-SQL compliance, and for clearly marking deviations from ANSI-SQL in their reference documentation.