Mysql SELECT inside UPDATE

Question

UPDATE forms SET

pos = (SELECT MIN(pos)-1 FROM forms)

WHERE id=$id

This doesn\'t work, error message:

**You can\'t specify target         


        

Answer 1

You could also try:

START TRANSACTION;
SET @newMin := MIN(pos)-1 FROM forms;
UPDATE forms SET pos=@newMin WHERE id='$id';
COMMIT;

Answer 2

Your problem is stated plainly in the MySQL manual:

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

You'll want to use a transaction. Turn AutoCommit off, begin a transaction, then do a SELECT MIN(pos)-1 FROM forms FOR UPDATE, take that result, do the update with it, then commit your transaction.

Answer 3

Consp is right that it's not supported. There's a workaround, however:

UPDATE forms SET
pos = (SELECT MIN(pos)-1 FROM (SELECT * FROM forms) AS x)
WHERE id=$id

A version that is probably faster:

UPDATE forms 
SET pos = (SELECT pos-1 FROM (SELECT MIN(pos) AS pos FROM forms) AS x)
where id=$id

Answer 4

I think that you can not use a subquery inside an update statement, but any way there are workarounds for it ...

Here is a Quotation from the following site:

"dev.mysql.com"

“Currently, you cannot delete from a table and select from the same table in a sub-query ”