Delete statement with group by does not work

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May 5th, 2008, 09:32 AM

annlis1977

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Delete statement with group by does not work

Hi,

I have 2 tables:

* classified (id, title, status, ...)
* archive (id, classified_id, modification_date, ...)

An archive is a "log of the classifieds modifications".

I would like to delete all the data of a classified where its "status" is "deleted (3)" and where the maximum archive.modification_date is older than 1 year.

The SELECT statement works fine:

Code:

SELECT *
FROM archive a, classified c
WHERE c.status=3 AND a.classified_id = c.id
GROUP BY a.classified_id
HAVING MAX(a.modification_date) < '2007-04-28'

The DELETE statement is not working:

Code:

DELETE a, c
FROM archive a, classified c
WHERE c.status=3 AND a.classified_id = c.id
GROUP BY a.classified_id
HAVING MAX(a.modification_date) < '2007-04-28'

Is there any way to do it without creating a TEMP table?

Thanks for your help.

Best regards,
Fred

May 5th, 2008, 11:24 AM

Veamon

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If you have your foreign keys setup properly, and have it set to delete cascade, couldnt you do a

delete from classifieds where status = 3 and modification_date < '2007-04-28'

your archive should have a foreign key that relates it to the classifieds, then it should all go bye bye.

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May 5th, 2008, 12:06 PM

annlis1977

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Quote:

Originally Posted by Veamon

If you have your foreign keys setup properly, and have it set to delete cascade

Unfortunately the tables are not InnoDB => no FOREIGN KEYs.

May 5th, 2008, 12:33 PM

shammat

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Quote:

Originally Posted by annlis1977

I have 2 tables:

* classified (id, title, status, ...)
* archive (id, classified_id, modification_date, ...)

An archive is a "log of the classifieds modifications".

I would like to delete all the data of a classified where its "status" is "deleted (3)" and where the maximum archive.modification_date is older than 1 year.

I don't think it possible to DELETE from two tables in a single statement. So you have to split this up in two statements.
Something like this (untested!)

Code:

DELETE FROM archive
WHERE modification_date < '2007-04-28'
AND classified_id IN (SELECT id 
                      FROM classified 
                      WHERE status = 3);

DELETE FROM classified
WHERE status = 3;

May 5th, 2008, 02:46 PM

r937

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Quote:

Originally Posted by shammat

I don't think it possible to DELETE from two tables in a single statement.

but it is

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May 5th, 2008, 02:49 PM

r937

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Quote:

Originally Posted by annlis1977

I would like to delete all the data of a classified where ...

this sounds like you want to delete from only one table

your DELETE statement is attempting to delete from two

try something like

Code:

DELETE c -- only ;o)
FROM archive a, classified c
WHERE c.status=3 AND a.classified_id = c.id
GROUP BY a.classified_id
HAVING MAX(a.modification_date) < '2007-04-28'

caution: i'm not saying this is gonna work, i'm saying that if you only want to delete classified rows then that's the only table you should mention in the DELETE part, although of course you can still have a join in the FROM part

May 5th, 2008, 03:29 PM

shammat

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Quote:

Originally Posted by r937

but it is

Deleting rows from two tables in a single statement?
This must be a MySQL extension then, can you show me an example?

May 5th, 2008, 03:42 PM

annlis1977

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Quote:

Originally Posted by shammat

Deleting rows from two tables in a single statement?
This must be a MySQL extension then, can you show me an example?

Right, I wanted to deleted the rows from the 2 tables which is possible in MySQL.

http://dev.mysql.com/doc/refman/5.0/en/delete.html

"Currently, you cannot delete from a table and select from the same table in a subquery."

Maybe the "GROUP BY.... HAVING" is the same as a subquery...

May 5th, 2008, 04:36 PM

r937

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Quote:

Originally Posted by shammat

This must be a MySQL extension then

#10

May 6th, 2008, 01:19 PM

crazytrain81

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Makes sense that GROUP BY is equivalent contextually to using a subquery here - when you GROUP BY, you go from a set of individual rows to a single aggregated row - so the DELETE no longer has a set containing each row to be deleted, instead it has just a row of aggregate data.

If you're using 5 - using a procedure w/ a cursor. Select, then go through the cursor and delete rows.

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