Question

这就是我想要的东西（用想象的sql编写）：

SELECT A, B, C, AVG(  `Value` ) AS Value
FROM T 
GROUP BY A, B, C
HAVING AT LEAST TWO DIFFRENT C VALUES PER DISTINCT A,B 
ORDER BY A, B, C

是否可以在适当的mysql中重写这样的HAVING条件？

在First，我认为这会奏效：

    SELECT A, B, C, AVG(  `Value` ) AS Value
    FROM T 
    GROUP BY A, B, C
    HAVING COUNT(C)>2
    ORDER BY A, B, C

但它并不是因为对于相同的A，B，C组合不可能有2个不同的C值，所以你会怎么做？

Answer 1

您可以将查询分为两个不同的查询：

每个不同的A，B至少有两个不同的C值

select A, B
from T
group by A, B
having count(DISTINCT C)>1

您的最终查询

select  A, B, C, avg(Value)
from T
where
  (A, B) in (
    select A, B
    from T
    group by A, B
    having count(DISTINCT C)>1
  )
group by
  A, B, C

Answer 2

您可以尝试使用 WHERE 语句而不是 HAVING

SELECT A, B, C, AVG(  `Value` ) AS Value
FROM T 
WHERE 
     (
     SELECT COUNT(DISTINCT C)
     FROM T1
     WHERE T1.A = T.A AND T1.B = T.B
     ) >= 2
GROUP BY A, B, C
ORDER BY A, B, C

集团通过澄清

2 个答案: