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Date: Thu, 10 Sep 2009 08:08:57 -0700 (PDT)
From: "Knut Anders Hatlen (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-4374) Document the CROSS JOIN operation in
 the reference manual
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    [ https://issues.apache.org/jira/browse/DERBY-4374?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12753651#action_12753651 ] 

Knut Anders Hatlen commented on DERBY-4374:
-------------------------------------------

The description of the operation could say something similar to this (inspired by the wording used in the other JOIN operators):

A CROSS JOIN is a JOIN operation that produces the Cartesian product of two tables. Unlike other JOIN operators, it does not let you specify a join clause. You may however specify a WHERE clause in the SELECT statement.

Examples that we may provide:

SELECT * FROM T1 CROSS JOIN T2
which is equivalent to
SELECT * FROM T1, T2

and

SELECT * FROM T1 CROSS JOIN T2 WHERE T1.X = T2.X
which is equivalent to
SELECT * FROM T1 INNER JOIN T2 ON T1.X = T2.X

And perhaps we should have a more complex example. For instance:

SELECT * FROM T1 LEFT OUTER JOIN T2 CROSS JOIN T3 ON T1.X = T2.X WHERE T3.Z > 50

We should probably change the examples so that they use the same table names as the other JOIN examples.

> Document the CROSS JOIN operation in the reference manual
> ---------------------------------------------------------
>
>                 Key: DERBY-4374
>                 URL: https://issues.apache.org/jira/browse/DERBY-4374
>             Project: Derby
>          Issue Type: Improvement
>          Components: Documentation
>    Affects Versions: 10.6.0.0
>            Reporter: Knut Anders Hatlen
>
> CROSS JOIN was added in DERBY-4355. We should document it alongside the other join operations in the reference manual.

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