＃1241-操作数应包含1列

Question

In the following query am trying to get one image per category

SELECT  l.*
FROM    (
   SELECT  id AS category_id,
           COALESCE(
           (
           SELECT  *
           FROM    images li
           WHERE li.category_id = dlo.id

           ORDER BY
                       li.save_status DESC, li.category_id DESC, li.id DESC
           LIMIT 1
           ), 0) AS mid
   FROM    cats_imgs dlo where id='1'
   ) lo
JOIN    images l
ON      l.save_status = '3'
   AND l.category_id >= lo.category_id
   AND l.category_id <= lo.category_id
   AND l.id >= lo.mid

but keep getting the following error :

#1241 - Operand should contain 1 column(s)

Any ideas ?

Answer 1

用单个列替换* images li

Answer 2

I had a similar problem. Your 3rd level select statement ( SELECT * FROM images li ) needs to return a single value, since the 2nd level select statement ( SELECT id AS category_id,COALESCE( ... ) is expecting only one value in its place holder.

For my case, it worked. Here I also averaged the data from a second based table ( SecondBasis ) to the values in the one minute basis table ( MinuteBasis ):

SELECT MinuteBasis.time, MinuteBasis.avg_t, MinuteBasis.avg_p,MinuteBasis.avg_t2,
  (SELECT avg(SecondBasis.m1)
   FROM SecondBasis
   WHERE SecondBasis.time BETWEEN MinuteBasis.time AND addtime (MinuteBasis.time,'0 0:00:59'))
  (SELECT avg(SecondBasis.m2)
   FROM SecondBasis
   WHERE SecondBasis.time BETWEEN MinuteBasis.time AND addtime (MinutBasis.time,'0 0:00:59'))
FROM MinuteBasis
WHERE MinuteBasis.time BETWEEN '2012-05-02 8:30:00' AND '2012-05-02 8:44:59' ;