Informix SQL and ANSI SQL

The Informix® implementation of SQL is compatible with standard SQL. Informix SQL is also compatible with the IBM® version of the language. However, Informix SQL contains extensions to the standard; that is, extra options or features for certain statements, and looser rules for others. Most of the differences occur in the statements that are not in everyday use. For example, few differences occur in the SELECT statement, which accounts for 90 percent of SQL use.

When a difference exists between Informix SQL and ANSI standard, the Informix Guide to SQL: Syntax identifies the Informix syntax as an extension to the ANSI standard for SQL.