Question

I have a correlated subquery in an update that used to work just fine (last year it worked; this year I made some small changes to the schema and the data are different). Now it fails with “Subquery returns more than 1 row” error.

The query is this:

update mytable as q
set p_ID = (
  select ap.pID
    from aptable as ap
    where ap.ID = q.ID
      and ap.txnDate is not NULL
      order by ap.txnDate
      limit 1 offset 2
   )

Weird, eh?

To find where it returns more than one row – which should be impossible, I prepared the query with the addition of “where ap.ID = ?” and ran the query in a loop for each valid ID value. Guess what – it worked all the way through.

Any ideas of what’s going on here?

Answer 1

I’m guessing it’s due to Bug #20519: “‘Subquery returns more that 1 row’ error with ‘limit x, 1′”, which was fixed in MySQL 5.0.25.