Mysql SELECT di dalam UPDATE

Consp benar bahwa itu tidak didukung. Namun ada solusinya:

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

Versi yang mungkin lebih cepat:

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