QUEL query languages

QUEL is a relational database query language, based on tuple relational calculus, with some similarities to SQL. 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.

Eugene Wong of Ingres was the creator of QUEL. As Oracle and IBM DB2 gained market share in the early 1980s, Ingres and other companies supporting QUEL moved to SQL. 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. Consider this example, taken from one of the first original Ingres papers:

Here E is a tuple variable that ranges over the EMPLOYEE relation, and all tuples in that relation are found which satisfy the qualification E.Name = "Jones". The result of the query is a new relation W, which has a single domain COMP that has been calculated for each qualifying tuple. Additional queries can then be made against the relation W.

An equivalent SQL statement is:

In this example, the relation is being stored in a new table W. This is not a direct analog of the QUEL version; relations in QUEL are more similar to temporary tables seen in most modern SQL implementations.

Here is a sample of a simple session that creates a table, inserts a row into it, and then retrieves and modifies the data inside it and finally deletes the row that was added (assuming that name is a unique field).

Another feature of QUEL was a built-in system for moving records en-masse into and out of the system. Consider this command: