[jira] Commented: (DERBY-4374) Document the CROSS JOIN operation in the reference manual

["Knut Anders Hatlen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-4374?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12761183#action_12761183 ] 

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

Thanks Kim! The docs look great.

I'm wondering if we should add a note about the ON clause to the more complex example. Users may be confused since we say that CROSS JOIN doesn't let you specify a join clause (aka ON/USING), whereas the example appears to be showing just that; a CROSS JOIN with an ON clause. What about adding another example below it and say something like

----
Note that the ON clause in the example above is associated with the LEFT OUTER JOIN operator, not with the CROSS JOIN operator, and it is therefore equivalent to the following statement:

SELECT * FROM CITIES LEFT OUTER JOIN
    (FLIGHTS CROSS JOIN COUNTRIES)
        ON CITIES.AIRPORT = FLIGHTS.ORIG_AIRPORT 
            WHERE COUNTRIES.COUNTRY_ISO_CODE = 'US'
----

The parentheses will hopefully make it clearer how the previous example could be correct even if it apparently had a CROSS JOIN + ON, and it'll additionally show that parens are allowed around the join operations.

> 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
>            Assignee: Kim Haase
>         Attachments: DERBY-4374.diff, DERBY-4374.stat, DERBY-4374.zip
>
>
> CROSS JOIN was added in DERBY-4355. We should document it alongside the other join operations in the reference manual.

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