Object Query Language
Encyclopedia
Object Query Language is a query language
standard for object-oriented databases
modeled after SQL
. OQL was developed by the Object Data Management Group (ODMG). Because of its overall complexity no vendor has ever fully implemented the complete OQL. OQL has influenced the design of some of the newer query languages like JDOQL and EJB QL
, but they can't be considered as different flavors of OQL.
database:
on a PC
, grouped by manufacturer:
Note the use of the keyword
.
Query language
Query languages are computer languages used to make queries into databases and information systems.Broadly, query languages can be classified according to whether they are database query languages or information retrieval query languages...
standard for object-oriented databases
Object database
An object database is a database management system in which information is represented in the form of objects as used in object-oriented programming...
modeled after SQL
SQL
SQL is a programming language designed for managing data in relational database management systems ....
. OQL was developed by the Object Data Management Group (ODMG). Because of its overall complexity no vendor has ever fully implemented the complete OQL. OQL has influenced the design of some of the newer query languages like JDOQL and EJB QL
EJB QL
EJB QL or EJB-QL is a portable database query language for Enterprise Java Beans. It was used in Java EE applications. Compared to SQL, however, it is less complex but less powerful as well.-History:...
, but they can't be considered as different flavors of OQL.
General Rules of OQL
The following rules apply to OQL statements:- All complete statements must be terminated by a semi-colon.
- A list of entries in OQL is usually separated by commas but not terminated by a comma.
- Strings of text are enclosed by matching quotation marks.
Simple query
The following example illustrates how one might retrieve the CPU-speed of all PCs with more than 64MB of RAM from a fictional PCPersonal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
database:
SELECT pc.cpuspeed
FROM PCs pc
WHERE pc.ram > 64
Query with grouping and aggregation
The following example illustrates how one might retrieve the average amount of RAMRam
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
on a PC
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
, grouped by manufacturer:
SELECT manufacturer, AVG(SELECT part.pc.ram FROM partition part)
FROM PCs pc
GROUP BY manufacturer: pc.manufacturer
Note the use of the keyword
partition, as opposed to aggregation in traditional SQLSQL
SQL is a programming language designed for managing data in relational database management systems ....
.
See also
- ODMG - Object Data Management Group
- Object Definition LanguageObject Definition LanguageObject Definition Language is the specification language defining the interface to object types conforming to the ODMG Object Model...