在查詢中使用從子查詢定義的列

Question

我需要使用從SEATS_RESERVED獲得的值。 下面的查詢為我提供了無效的列名稱“ SEATS_RESERVED”錯誤。

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

您不能在SELECT中創建派生字段並在WHERE子句中引用它。

有幾種解決方法，這是對查詢的更改最少的一種。

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

您正在嘗試將SEATS_RESERVED設置為等於子查詢中的值，但尚未聲明SEATS_RESERVED。 另外，MAX_SEATS在哪里定義？

這個怎么樣：

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 = ?