Entry

Database: SQL: Query: Operation: Join: What is a join query?

Feb 3rd, 2007 17:06
Knud van Eeden,

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--- Knud van Eeden --- 19 March 2005 - 10:52 pm ----------------------

Database: SQL: Query: Operation: Join: What is a join query?

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A database manager can join two tables by matching the primary keys in
one table to the foreign keys in another.

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Sometimes you have to select data from two or more tables to make your
result complete. Then you have to perform a join.

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Joins are used to select and combine information from two or
more columns in two or more tables.

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The tables you want to join must have at least one column in common
(e.g. the primary key column in the first table, and the corresponding
foreign key column in the second table)

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A join query is a querying technique that
matches rows from two or more tables
based on a join condition
in a WHERE clause.

That query then outputs only those rows that meet the condition.

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Book: see also:

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[book: author: Lane, David / Williams, Hugh E. - title: Web Database 
Applications with PHP & MySQL - publisher: O'Reilly - ISBN: 0-596-
00041-3 - pages total: 582]

[book: author: Hibbs, Curt / Tate, Bruce A. - title: Ruby on Rails: Up 
and Running - publisher: O'Reilly - year: 2006 - ISBN 978-0-59-610132-
9 - 'Relational Database Relationships']

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Internet: see also:

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[Internet: see also: http://www.google.com search for 'database 
relational create unique insert id concatenate': 
http://www.perlhelp.com/sams/Sams_Chapters/0672322609/]

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Database: Language: SQL: Overview: Can you give an overview of links 
about SQL?
http://www.faqts.com/knowledge_base/view.phtml/aid/32811/fid/54

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