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?
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/
来源：https://stackoverflow.com/questions/21813895/where-can-i-find-sql-language-specification