What the best resource to learn ANSI SQL? [closed]

I don't mean "Basic SQL", but strongly the specs and the difference between the specs and the implementations between great databases (like SQL Server, Oracle, etc).

Which tool is good for learning SQL?

You can watch SQLZOO, Codecademy, and several other tutorials that will provide you with the best educators for SQL and also test your SQL knowledge. You can also take classes for SQL which will enlighten you not only for basics but also for advanced and certification levels.

Which database do you use ANSI SQL?

Since Oracle 9i, Oracle SQL supports the ANSI SQL syntax.

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SQL In a Nutshell by O'Reilly and Associates. It covers all 5 major SQL Dialects, the differences between them, and does that for each function/feature listed. (ANSI SQL99, Oracle, MySql, Postgres, and SQL Server).