It was created as a part of the Ingres DBMS effort at University of California, Berkeley, based on Codd's earlier suggested but not implemented Data Sub-Language ALPHA.
QUEL was used for a short time in most products based on the freely available Ingres source code, most notably in an implementation called POSTQUEL supported by POSTGRES.
[1] As Oracle and DB2 gained market share in the early 1980s, most companies then supporting QUEL moved to SQL instead.
[citation needed] QUEL continues to be available as a part of the Ingres DBMS, although no QUEL-specific language enhancements have been added for many years.[when?]
QUEL statements are always defined by tuple variables, which can be used to limit queries or return result sets.