Actually, there are *lots* of SQL standards.
The one banded around most is SQL92 - and MS SQL Server is probably the DB which supports it closest (they make a big deal about it), but I can't think of a single DB that supports the full SQL92 standard.
Don't even get me started on the later SQL standards (96 is the latest, I think).
For a start, even MS SQL Server only sort of supports the INFORMATION_SCHEMA user and the various views/etc which go with that.
On top of that, what you say is true - each DB has it's own extensions on top of the SQL standards - functions, packages, aggregation, etc. There is a massive list of additional options - and everyone says their implementation is the best.
Cheers,
Paul.
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