SQL is a programming language specifically used for relational databases. SQL is not supported by Data Services but provided below are some resources for learning SQL.
Common database management systems (DBMS) include Oracle, PostgreSQL, SQLite, MySQL and Microsoft SQL Server. Each system has it's own syntax intricacies but learning standard SQL first should be a good start before learning the specifics of any system. XAMPP is a PHP development enviornment which can be used as a testing enviornment for learning SQL. (See Lynda.com tutorial below.)