[TYPO3-core] FYI #14182: Multiple join conditions are not supported

[Jigal van Hemert]

Xavier Perseguers wrote:
> $rec = $GLOBALS['TYPO3_DB']->exec_SELECTquery(
>     '*',
>     'T1 LEFT OUTER JOIN T2 ON T2.pid=T1.uid AND T2.size=4',
>     'T1.cr_userid=1'
> );
> 
> Problem is that this query cannot be rewritten due to the T2.size=4 
> which cannot be moved to the WHERE clause and cannot be left alone as 
> left outer join condition.

Just curious, as it might be different for other DBMS-s:
why can't you move it to the WHERE clause? The MySQL manual only says: 
"The conditional_expr used with ON is any conditional expression of the 
form that can be used in a WHERE  clause. Generally, you should use the 
ON  clause for conditions that specify how to join tables, and the WHERE 
clause to restrict which rows you want in the result set."

There is 'should' in the text, not 'must'. The ON condition can be put 
in the WHERE clause, but it might perform better if the conditions are 
in the correct ON clause.

[1] http://dev.mysql.com/doc/refman/5.1/en/join.html

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Jigal van Hemert
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