Running select statement inside an update query

Running select statement inside an update query



You could use a non-correlated subquery to do the work for you:


1.  UPDATE tbl_1 dest,
(SELECT count(*) as cnt_n,userid FROM tbl_2 group by userid) src
 SET dest.cnt = src.cnt_n
where dest.id = src.userid



2. UPDATE  tbl_taxclasses c
INNER JOIN
( SELECT  COUNT(regionsid) AS n  FROM  tbl_taxclasses_regions GROUP BY   classid ) r
USING(classid)
SET
c.regionscount = r.n
WHERE
c.classid = 1



3. UPDATE `tbl_taxclasses`
 SET `regionscount` = (
  SELECT COUNT(regionsid) AS `num`
  FROM `tbl_taxclasses_regions`
  WHERE classid = 1)
 WHERE classid = 1 LIMIT 1



4.UPDATE table1 dest, (SELECT * FROM table2 where id=x) src
  SET dest.col1 = src.col1 where dest.id=x ;