mySQL中的嵌套select语句

Question

我有一个现有的SQL查询在SQL Server中正常工作，我想在MySQL中工作。我把它清理了一下，用列表/表格名称等的后退标记来摆弄，但无法使其工作。

这里是有问题的声明：

SELECT `EmployeeID` 
FROM `Employee` 
WHERE 
(
    (
     SELECT COUNT(*) AS A 
     FROM `TimeClock` 
     WHERE (`EmployeeID` = `Employee.EmployeeID`) 
     AND (`InOut` = 'True') 
    ) > (
     SELECT COUNT(*) AS B 
     FROM `TimeClock` AS `TimeClock_1` 
     WHERE (`EmployeeID` = `Employee.EmployeeID`) 
     AND (`InOut` = 'False') 
    ) 
) 

这应该返回必须在TimeClock表的详细InOut = True超过InOut = False任何EmployeeID的。

谢谢。

Answer 1

这应该为您提供那里是InOut真不是假

SELECT e.EmployeeId 
FROM Employee AS e 
INNER JOIN 
(
    SELECT tc.EmployeeID 
     , SUM(CASE 
       WHEN tc.InOut = 1 THEN 1 ELSE 0 
      END) AS InOutTrue 
     , SUM(CASE 
       WHEN tc.InOut = 0 THEN 1 ELSE 0 
      END) AS InOutFalse 
    FROM TimeClock AS tc 
    GROUP BY tc.EmployeeId 
) AS t ON e.EmployeeId = t.EmployeeId 
WHERE t.InOutTrue > t.InOutFalse 

我在我的很小没有索引的测试数据显示出类似的性能提出了两个备选方案更值EmployeeId值。我建议你根据自己的数据对它们进行测试，看看它们是否有任何区别：

这一个是几乎相同，但使用总记录数而不是InOutFalse。

SELECT e.EmployeeId 
FROM Employee AS e 
INNER JOIN 
(
    SELECT tc.EmployeeID 
     , COUNT(1) AS RecordCount 
     , SUM(CASE 
       WHEN tc.InOut = 1 THEN 1 ELSE 0 
      END) AS InOutTrue 
    FROM TimeClock AS tc 
    GROUP BY tc.EmployeeId 
) AS t ON e.EmployeeId = t.EmployeeId 
WHERE t.InOutTrue > RecordCount - t.InOutTrue 

我不知道如果MySQL需要我这里使用的CAST，但SQL Server一样。 （这是我测试过的）它不能在BIT列上执行SUM。

SELECT e.EmployeeId 
FROM Employee AS e 
INNER JOIN TimeClock AS tc ON e.EmployeeId = tc.EmployeeId 
GROUP BY e.EmployeeId 
HAVING SUM(CAST(tc.InOut AS INT)) > (COUNT(1) - SUM(CAST(tc.InOut AS INT))) 

如果三者的表现相似，则归结为个人偏好。