Since joins require knowledge of the underlying schema to get right, you probably want to expose database views rather than implement join syntax. Regular users

Since joins require knowledge of the underlying schema to get right, you probably want to expose database views rather than implement join syntax. Regular users aren't going to understand joins or get them right no matter how simple you make the syntax. I wrote a report generator for end users that uses simplified syntax, and found it was useful to present a standard list of column names rather than the actual names, and to hide the joins altogether. Views can accomplish most of that, especially in a query-only application.