The SQL SELECT statement returns a result set of records from one or more tables.A SELECT statement retrieves zero or more rows from one or more database tables or database views. In most applications, SELECT is the most commonly used Data Manipulation Language command...
A hierarchical database model is a data model in which the data is organized into a tree-like structure. The structure allows representing information using parent/child relationships: each parent can have many children, but each child has only one parent...
A Common Table Expression, or CTE, is a temporary named result set, derived from a simple query and defined within the execution scope of a SELECT, INSERT, UPDATE, or DELETE statement....
(CTEs). Recursive CTEs are supported by systems including IBM DB2
IBM DB2
The IBM DB2 Enterprise Server Edition is a relational model database server developed by IBM. It primarily runs on Unix , Linux, IBM i , z/OS and Windows servers. DB2 also powers the different IBM InfoSphere Warehouse editions...
Microsoft SQL Server is a relational database server, developed by Microsoft: It is a software product whose primary function is to store and retrieve data as requested by other software applications, be it those on the same computer or those running on another computer across a network...
Firebird is an open source SQL relational database management system that runs on Linux, Windows, and a variety of Unix. The database forked from Borland's open source edition of InterBase in 2000, but since Firebird 1.5 the code has been largely rewritten ....
PostgreSQL, often simply Postgres, is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, MS Windows and Mac OS X. It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software...
CUBRID is a comprehensive open source relational database management system highly optimized for Web applications, especially when complex business services process large amount of data and generate huge concurrent requests...
.
An alternative syntax is the non-standard CONNECT BY construct.
EnterpriseDB is a privately held company that provides enterprise class support for PostgreSQL through its product Postgres Plus Standard Server, which is PostgreSQL with extra bundled modules...
CUBRID is a comprehensive open source relational database management system highly optimized for Web applications, especially when complex business services process large amount of data and generate huge concurrent requests...
. Example query:
SELECT select_list
FROM table_expression
[ WHERE ... ]
[ START WITH start_expression ]
CONNECT BY { PRIOR parent_expr = child_expr | child_expr = PRIOR parent_expr }
[ ORDER SIBLINGS BY column1 [ ASC | DESC ] [, column2 [ ASC | DESC ] ] ...
[ GROUP BY ... ]
[ HAVING ... ]
...
For example:
SELECT LEVEL, LPAD (' ', 2 * (LEVEL - 1)) || ename "employee", empno, mgr "manager"
FROM emp START WITH mgr IS NULL
CONNECT BY PRIOR empno = mgr;
