As its name implies, SQL is used to express a database query. SQL has facilities for defining which fields should be returned from the query, if and how the query should be filtered and sorted, and so on. Although SQL is an industry standard language, various specific versions and editions of the standard are implemented by SQL-based databases. Crystal Reports does not use just a single syntax, but rather is robust enough to handle most major SQL language derivations. The rest of this appendix walks you through the SQL Language and points out specific areas that are of concern to Crystal Reports. Although it doesn't focus on a specific version of SQL, it does point out differences where appropriate.