Question

i am doing this:

delete from calibration_2009 where rowid in
(SELECT rowid FROM `qcvalues`.`batchinfo_2009` where reporttime like "%2010%");

i need to have about 250k rows deleted.

why does it take such a long time? is there a quicker way to do this?

Answer 1

DELETE  c
FROM    `qcvalues`.`batchinfo_2009` b
JOIN    calibration_2009 c
ON      c.rowid = b.rowid
WHERE   b.reporttime LIKE '%2010%';

You should have an index on calibration_2009 (rowid) for this to work fast.

I assume it’s a PRIMARY KEY anyway, but you better check.