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QUEL is a relational database access language, similar in most ways to SQL. It was created as a part of the Ingres 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 Informix.^{[citation needed]} As Oracle and DB2 started taking over the market 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 today, although no QUEL-specific language enhancements have been added for many years.

[edit] Usage

QUEL statements are always defined by tuple variables, which can be used to limit queries or return result sets. Consider this example, taken from the original Ingres paper:

 range of e is employee retrieve (comp = e.salary/ (e.age - 18)) where e.name = "Jones" 

e is a tuple, defining a set of data, in this case all the rows in the employee table that have the first name "Jones". An equivalent SQL statement is:

 select (e.salary/ (e.age - 18)) as comp from employee as e where e.name = "Jones" 

QUEL is generally more "normalized" than SQL.^{[citation needed]} Whereas every major SQL command has a format that is at least somewhat different from the others, in QUEL a single syntax is used for all commands.^{[citation needed]}

For instance, 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).

 create student(name = c10, age = i4, sex = c1, state = c2) range of s is student append to s (name = "philip", age = 17, sex = "m", state = "FL") retrieve (s.all) where s.state = "FL" replace s (age=s.age+1) retrieve (s.all) delete s where s.name="philip" 

Here is a similar set of SQL statements:

 create table student(name char(10), age int, sex char(1), state char(2)) insert into student (name, age, sex, state) values ('philip', 17, 'm', 'FL') select * from student where state = 'FL' update student set age=age+1 select * from student delete from student where name='philip' 

Note that every command uses a unique syntax, and that even similar commands like INSERT and UPDATE use completely different styles.

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

 copy student(name=c0, comma=d1, age=c0, comma=d1, sex=c0, comma=d1, address=c0, nl=d1)
 into "/student.txt" 

I which creates a comma-delimited file of all the records in the student table. The d1 indicates a delimiter, as opposed to a data type. Changing the into to a from reverses the process. Similar commands are available in many SQL systems, but usually as external tools, as opposed to being internal to the SQL language. This makes them unavailable to stored procedures.

QUEL has an extremely powerful aggregation capability. Aggregates can be nested, and different aggregates can have independent by-lists and/or restriction clauses. For example:

  retrieve (a=count(y.i by y.d where y.str = "ii*" or y.str = "foo"),b=max(count(y.i by y.d))) 

This example illustrates one of the arguably less desirable quirks of QUEL, namely that all string comparisons are potentially pattern matches. y.str = "ii*" matches all y.str values starting with ii.

[edit] See also

• Tutorial D
• D (data language specification)
• D4 (programming language) (an implementation of D)
• Relational algebra
• Relational calculus

[edit] External links

• Non SQL Query Languages, by Antoni Kokot and David West
• C. J. Date: A Critique of the SQL Database Language. SIGMOD Record 14(3): 8-54, 1984.

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