Question

我需要使用从SEATS_RESERVED获得的值。下面的查询给我一个无效的列名称'SEATS_RESERVED'错误。

SELECT *,
SEATS_RESERVED =
(SELECT COUNT(UID)
FROM person WHERE person.RES_DATE = reservation_dates.RES_DATE 
AND person.ARCHIVE = 'FALSE')
FROM reservation_dates
WHERE TERM = ?
AND SEATS_RESERVED < MAX_SEATS;

Answer 1

您无法在SELECT 中创建派生字段，而在WHERE子句中引用它。

有几种方法可以解决这个问题，其中一个选项对查询的更改最少。

SELECT * FROM
(
  SELECT *,
  SEATS_RESERVED =
  (SELECT COUNT(UID)
  FROM person WHERE person.RES_DATE = reservation_dates.RES_DATE 
  AND person.ARCHIVE = 'FALSE')
  FROM reservation_dates
  WHERE TERM = ?
)
  AS data
WHERE SEATS_RESERVED < MAX_SEATS;

Answer 2

您尝试将SEATS_RESERVED设置为等于子查询中的值，但尚未声明SEATS_RESERVED。另外，MAX_SEATS定义在哪里？

这个怎么样：

DECLARE @MAX_SEATS INT
SET @MAX_SEATS = <some integer>


SELECT *,
   (SELECT COUNT(UID) FROM person WHERE person.RES_DATE = reservation_dates.RES_DATE 
AND person.ARCHIVE = 'FALSE' HAVING COUNT(UID) < @MAX_SEATS;) AS SEATS_RESERVED
FROM reservation_dates
WHERE TERM = ?

在查询中使用从子查询定义的列

2 个答案: