Question

我正在努力制作奖励系统中前20名收入者的名单。

以下陈述完美地表明：

SELECT
    S.User_ID As UserID,
    CONCAT(S.User_Forename, " ", S.User_Surname) AS StudentName,
    T.TotalPoints
FROM
    student S
INNER JOIN 
    ( SELECT
        Datetime, Recipient_ID, SUM(Points) AS TotalPoints
      FROM
        transactions
      GROUP BY
        Recipient_ID ) T
ON
    S.User_ID = T.Recipient_ID
ORDER BY TotalPoints DESC
LIMIT 20

然而，想想看，明年，我需要包括一个日期范围（即仅显示该学年的最高收入者）。

出于测试目的，我尝试修改以下声明，其中包括LESS THAN DATETIME选择：

SELECT
    S.User_ID As UserID,
    CONCAT(S.User_Forename, " ", S.User_Surname) AS StudentName,
    T.TotalPoints
FROM
    student S
INNER JOIN 
    ( SELECT
        Datetime, Recipient_ID, SUM(Points) AS TotalPoints
      FROM
        transactions
      GROUP BY
        Recipient_ID ) T
ON
    S.User_ID = T.Recipient_ID
WHERE t.Datetime < 2012-03-20
ORDER BY TotalPoints DESC
LIMIT 20

我也试过这个：

SELECT
    S.User_ID As UserID,
    CONCAT(S.User_Forename, " ", S.User_Surname) AS StudentName,
    T.TotalPoints
FROM
    student S
INNER JOIN 
    ( SELECT
        Datetime, Recipient_ID, SUM(Points) AS TotalPoints
      FROM
        transactions
      WHERE Datetime < 2012-03-20
      GROUP BY
        Recipient_ID ) T
ON
    S.User_ID = T.Recipient_ID
ORDER BY TotalPoints DESC
LIMIT 20

但这两个都显示空结果集。

如果我做一个简单的SELECT * FROM transactions WHERE Datetime < 2012-03-20，则返回超过25K的结果。

我哪里错了？

Answer 1

您的日期值似乎缺少单引号'：

WHERE t.Datetime < '2012-03-20'

将日期合并到此GROUP BY和INNER JOIN选择语句中

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