用子查询联接中更新

Question

UPDATE item t 

INNER JOIN ( SELECT
               item_name,
               MAX( item_keyword ) AS item_keyword
             FROM item
             WHERE ca_id2  = '2010'
             GROUP BY item_name
           ) s ON t.item_name = s.item_name

SET t.item_keyword = s.item_keyword 

WHERE t.ca_id2 ='3010'

The error is:

1064 - You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT item_name, max(item_keyword) AS item_keyword FROM item

MySQL version 4.0.22 What is the reason for the failure?

Answer 1

I tried to construct your query based on http://www.xaprb.com/blog/2006/06/23/how-to-select-from-an-update-target-in-mysql/

UPDATE item t

SET t.item_keyword =
      ( SELECT MAX( i.item_keyword ) AS item_keyword
          FROM ( SELECT item_keyword, item_name, cd_id2 FROM item ) AS i
         WHERE t.item_name = i.item_name
           AND i.cd_id2  = '2010'
      GROUP BY i.item_name
      )

WHERE t.ca_id2 ='3010'

Or you can try this version too

UPDATE item t

INNER JOIN ( SELECT item_keyword, item_name, cd_id2 FROM item ) AS i

SET t.item_keyword =
      ( SELECT MAX( i.item_keyword ) AS item_keyword
          FROM i
         WHERE t.item_name = i.item_name
           AND i.cd_id2  = '2010'
      GROUP BY i.item_name
      )

WHERE t.ca_id2 ='3010'

Sorry, I don't have MySQL 4 around, so you have to test the above queries.

Other readings:

• http://dev.mysql.com/doc/refman/4.1/en/update.html
• http://dev.mysql.com/doc/refman/4.1/en/rewriting-subqueries.html

If the above queries don't work, you can try using a temporary table instead of the subselect:

http://sqlfiddle.com/#!2/13ccb/1

CREATE TEMPORARY TABLE s
   SELECT item_name,
          MAX( item_keyword ) AS item_keyword
    FROM  item
    WHERE cd_id2  = '2010'
      AND item.item_name IN ( SELECT item_name FROM item WHERE item.ca_id2='3010')
GROUP BY item_name;


UPDATE item t 
INNER JOIN s ON t.item_name = s.item_name
SET t.item_keyword = s.item_keyword 
WHERE t.ca_id2 ='3010';

DROP TEMPORARY TABLE s;