Where can I find SQL language specification

问题:

Is there an official SQL standard? I.e. I want to understand what type of expression is supported by SQL language and how this expression evaluated by server? What documents are using for implementation SQL based databases?

回答1:

There is an official SQL standard from the ISO/ANSI committee.

Some information can be found here: http://en.wikipedia.org/wiki/Sql

However the specification itself is not freely available. You might find some drafts of older specs in the internet if you search for it.

A nice explanation of the (yet a bit old) ANSI 99 standard is here: https://mariadb.com/kb/en/sql-99-complete-really/