Question

I am at loss to figure out how to do an UPDATE with CASE and JOIN. This example is from my Drupal database. content_type has nid as its primary key; term_node, on the other hand, can have multiple rows with the same nid matched to different tids. MySQL will happily parse a query based on WHERE:

UPDATE `content_type`
LEFT JOIN `term_node` USING(nid)
 SET
  `field_m03` = 1
   WHERE tid = 696;

The above updates all rows in content_type which have an nid matched to (tid = 696) in term_node, as it should.
But when I try to string several conditions with CASE it won’t work. No errors, but 0 rows affected:

UPDATE `content_type`
LEFT JOIN `term_node` USING(nid)
 SET
  `field_m03` = (CASE
   WHEN (tid = '696') THEN '1'
   WHEN (tid = '697') THEN '2'
   WHEN (tid = '698') THEN '3'
   WHEN (tid = '699') THEN '4'
   WHEN (tid = '700') THEN '5'
   ELSE `field_m03`
   END);

Also tried without the parentheses and single quotes, no change.

Answer 1

Your syntax seems correct.

If your MySQL server has safe updates (SQL_SAFE_UPDATES) turned on, then your server will abort any updates that don’t have a WHERE or LIMIT clause.