MySQL CASE和INNER一起加入？

Question

我有以下SQL查询。

SELECT MIN(PLD.available_date) as 'FROM', MAX(PLD.available_date) as 'UNTIL', (
CASE
    WHEN DATEDIFF('2012-04-01', '2012-04-10') = (COUNT(PLD.available_date) - 1)
    THEN 'Yes'
    ELSE 'No'
END) as isAvailable, PL.*
FROM `parking_lot_dates` as PLD
INNER JOIN parking_lots as PL ON PLD.plid = PL.plid
WHERE PLD.available_date BETWEEN '2012-04-01' AND '2012-04-10'
GROUP BY PLD.plid

但是有可能将INNER JOIN放入CASE吗？ 我想要完成的是当isAvailable列的值为Yes时，然后获取额外的信息，否则不要抓住它。

我尝试将INNER JOIN放在CASE语句之间，但它没有用。

提前致谢。

Answer 1

您无法以您希望的方式进行条件连接，但您可以改为：

SELECT PLD.FROM, PLD.UNTIL, IF(PLD.isAvailable, 'Yes', 'No') AS isAvailable, PL.*
FROM (
    SELECT   plid
      ,      MIN(available_date) AS `FROM`
      ,      MAX(available_date) AS `UNTIL`
      ,      DATEDIFF('2012-04-01', '2012-04-10') = COUNT(*) - 1 AS `isAvailable`
    FROM     parking_lot_dates
    WHERE    available_date BETWEEN '2012-04-01' AND '2012-04-10'
    GROUP BY plid
  ) AS PLD LEFT JOIN parking_lots AS PL ON (
    PLD.isAvailable AND PL.plid = PLD.plid
  )
WHERE NOT (PLD.isAvailable AND PL.plid IS NULL)

子查询执行的分组操作parking_lot_dates表，我们做一个外在于和之间的连接parking_lots为了表有记录，即使加入条件不满足 。 了解SQL连接 。

WHERE子句通过消除任何预期在parking_lots没有匹配记录的结果来模仿INNER JOIN的效果; 如果你实际上不想要这种行为，它可以省略。

Answer 2

目前还不是很清楚你想要什么。 也许你需要一个HAVING子句：

SELECT PL.*
FROM parking_lot_dates AS PLD
  INNER JOIN parking_lots AS PL 
    ON PLD.plid = PL.plid
WHERE PLD.available_date BETWEEN '2012-04-01' AND '2012-04-10'
GROUP BY PLD.plid
HAVING DATEDIFF('2012-04-01', '2012-04-10') = COUNT(PLD.available_date) - 1