sql - If there are more than x Then where 语句

Question

无论如何，有没有让 HAVING 和 WHERE 子句相互猜想？即伪代码：

CASE
   HAVING count(children) > 3 THEN WHERE nationality = 'Mexican'
   HAVING count(children) = 2 THEN WHERE nationality = 'American'
   HAVING count(children) = 1 THEN WHERE nationality = 'Japanese'
END

Answer 1

您可以将查询包装在另一个SELECT

SELECT *
FROM
(
    SELECT count(children) as ChildrenCount, nationality 
    FROM yourTable
    GROUP BY nationality 
) x
WHERE 
    (ChildrenCount > 3 AND nationality = 'Mexican')
    OR
    (ChildrenCount = 2 AND nationality = 'American')
    OR
    (ChildrenCount = 1 AND nationality = 'Japanese')

Answer 2

你想要的逻辑是什么？

让我猜猜你想要有 3 个以上孩子的墨西哥人、有 2 个孩子的美国人和有 1 个孩子的日本人。在这种情况下，你会这样：

having (case when count(nationality = 'Mexican' then children end) > 3 then 'true'
             when count(nationality = 'American' then children end) = 2 then 'true'
             when count(nationality = 'Japanese' then children end) = 1 then 'true'
        end) = 'true'

然而，即使这看起来也很奇怪。为什么要数“孩子”。你在分组什么？如果 children 只是数据中的一个字段，那么这应该是 WHERE 子句而不是 HAVING 子句：

where (nationality = 'Mexican' and children end > 3) or
      (nationality = 'American' and children = 2) or
      (nationality = 'Japanese' and children = 1)

Answer 3

这应该有效

DECLARE @table TABLE     
(    
     nationality varchar (25),  
     totalchildren int
)   

insert @table  
    SELECT nationality,COUNT(children) AS totalchildren 
    FROM TABLENAME
    GROUP BY nationality

SELECT
    *
FROM
    @table  
WHERE 
    nationality = 
    (
        CASE 
            WHEN totalchildren > 3 THEN 'Mexican'
            WHEN totalchildren = 2 THEN 'American'
            WHEN totalchildren = 1 THEN 'Japanese' 
        END
    )

Answer 4

您可以将现有查询包装在 CTE 中，以将计数和分组与过滤分开，然后在带有 CASE 的最终 WHERE 子句中使用 CTE 中的计数：

;WITH [Counts] AS
(
    SELECT
        ,nationality
        ,COUNT(children) AS [children]
    FROM
        xyz
    GROUP BY
        nationality
)
SELECT
    *
FROM
    [Counts]
WHERE 
    nationality = 
    (
        CASE 
            WHEN [children] > 3 THEN 'Mexican'
            WHEN [children] = 2 THEN 'American'
            WHEN [children] = 1 THEN 'Japanese' 
        END
    )