On Wednesday 22 January 2003 19:39, Bill Rausch wrote:
> I've inherited a busted database and need to clean it up. I can't
> figure out how to do something which seemingly should be simple.
>
> For example, I've got two tables:
>
> Table One
> id int primary key auto_increment not null
> ...other data
>
> Table Two
> id int primary key auto_increment not null
> ...other data
>
> I'd like to delete all of the records from Table Two which have an id
> that is not found in Table One.
>
> I could do it programatically in C or PHP or ... but is there some
> kind of SQL statement than can do the job?
You can do it in version 4.0 and up, like
DELETE t2 FROM t2 LEFT JOIN t1 ON t2.id=t1.id WHERE t1.id IS NULL;
or since 4.0.2 like
DELETE FROM t2 USING t2 LEFT JOIN t1 ON t2.id=t1.id WHERE t1.id IS NULL;
for more info check the following section of the manual:
http://www.mysql.com/doc/en/DELETE.html
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