MySQL:FROM 子句中的子查询

Question

我正在尝试创建一个 View ，但我一直收到错误消息，指出 FROM 子句中的子查询

需要创建这些 View

SELECT EPC_ploc, COUNT(EPC_ploc)
FROM P_HAS_LOC
GROUP BY EPC_ploc
HAVING COUNT(EPC_ploc) =
(   
    SELECT MAX(mycount)
    FROM
    (
        SELECT EPC_ploc, COUNT(EPC_ploc) mycount
        FROM P_HAS_LOC
        GROUP BY EPC_ploc
    ) AS mycountt
)

和

SELECT Category_ID_h, COUNT(Category_ID_h)
FROM P_HAS_CA GROUP BY Category_ID_h
HAVING COUNT(Category_ID_h) = 
(   
    SELECT MAX(mycount)
    FROM
    (
        SELECT Category_ID_h, COUNT(Category_ID_h) mycount
        FROM P_HAS_CA
        GROUP BY Category_ID_h) AS mycountt
    )
)

Answer 1

我认为您需要重新处理查询中的子查询，这会导致所有问题。你应该能够摆脱这个:

SELECT EPC_ploc, COUNT(EPC_ploc)
FROM P_HAS_LOC
GROUP BY EPC_ploc
HAVING COUNT(EPC_ploc) =
(   
    SELECT COUNT(EPC_ploc)
    FROM P_HAS_LOC
    GROUP BY EPC_ploc
    ORDER BY COUNT(EPC_ploc) DESC
    LIMIT 1;
)

SELECT Category_ID_h, COUNT(Category_ID_h)
FROM P_HAS_CA
GROUP BY Category_ID_h
HAVING COUNT(Category_ID_h) = 
(   
    SELECT COUNT(Category_ID_h)
    FROM P_HAS_CA
    GROUP BY Category_ID_h
    ORDER BY COUNT(Category_ID_h)
    LIMIT 1;
)

正如@pala_ 提到的，您还可以使用 JOIN 重新处理您的查询，但我上面给出的是使用子查询获取所有组的最大值的一种正确方法。