mysql - 1242 - 子查询在子查询中返回多于 1 行

Question

我正在尝试获取每个员工的待处理金额总额。下面的查询工作正常:

SELECT SUM(amount) 
FROM pending
WHERE MONTH < DATE_SUB(curdate() , INTERVAL 1 MONTH) 
GROUP BY class

但是当我尝试将其添加为子查询时，它给出了以下错误:

1242 - Subquery returns more than 1 row

SELECT
  (period_diff(date_format(now(), '%Y%m'),
     date_format(MONTH, '%Y%m'))) AS months,
  pending.amount,
  pending.admission_numb,
  pending.month,
  staff.name,
  staff.class, (
    SELECT SUM(amount) 
    FROM pending
    WHERE MONTH < DATE_SUB(curdate(), INTERVAL 1 MONTH) 
    GROUP BY class
  )
FROM
  pending JOIN staff
  ON pending.admission_numb = staff.admission
GROUP BY admission
ORDER BY CAST( staff.class AS UNSIGNED ) , staff.class

任何帮助将不胜感激..

Answer 1

由于您的子查询返回不止一行(我希望它会为每个类返回一行)，因此您需要在 from 子句中加入您的子查询:

SELECT
  (period_diff(date_format(now(), '%Y%m'), date_format(MONTH, '%Y%m'))) AS months,
  pending.amount,
  pending.admission_numb,
  pending.month,
  staff.name,
  staff.class,
  sums.tot
FROM
  pending JOIN staff ON pending.admission_numb = staff.admission
  JOIN  (
    SELECT class, SUM(amount) as tot 
    FROM pending
    WHERE MONTH < DATE_SUB(curdate(), INTERVAL 1 MONTH)
    GROUP BY class
  ) sums on staff.class = sums.class
GROUP BY admission
ORDER BY CAST( staff.class AS UNSIGNED ) , staff.class