在一个 SQL 查询中使用不同条件从同一个表中查询多个聚合函数

Question

我正在创建一个 SQL 查询，该查询将根据两个聚合函数的值从表中提取记录。这些聚合函数从同一个表中提取数据，但过滤条件不同。我遇到的问题是 SUM 的结果比我只包含一个 SUM 函数要大得多。我知道我可以使用临时表创建此查询，但我只是想知道是否有一个只需要一个查询的优雅解决方案。

我创建了一个简化版本来演示这个问题。以下是表结构：

EMPLOYEE TABLE

EMPID
1
2
3

ABSENCE TABLE

EMPID   DATE       HOURS_ABSENT
1       6/1/2009   3
1       9/1/2009   1
2       3/1/2010   2

这里是查询：

SELECT
    E.EMPID
    ,SUM(ATOTAL.HOURS_ABSENT) AS ABSENT_TOTAL
    ,SUM(AYEAR.HOURS_ABSENT) AS ABSENT_YEAR

FROM
    EMPLOYEE E

    INNER JOIN ABSENCE ATOTAL ON
        ATOTAL.EMPID = E.EMPID

    INNER JOIN ABSENCE AYEAR ON
        AYEAR.EMPID = E.EMPID

WHERE
    AYEAR.DATE > '1/1/2010'

GROUP BY
    E.EMPID

HAVING
    SUM(ATOTAL.HOURS_ABSENT) > 10
    OR SUM(AYEAR.HOURS_ABSENT) > 3

任何见解将不胜感激。

Answer 1

SELECT
    E.EMPID
    ,SUM(ABSENCE.HOURS_ABSENT) AS ABSENT_TOTAL
    ,SUM(case when year(Date) = 2010 then ABSENCE.HOURS_ABSENT else 0 end) AS ABSENT_YEAR

FROM
    EMPLOYEE E

    INNER JOIN ABSENCE ON
        ABSENCE.EMPID = E.EMPID

GROUP BY
    E.EMPID

HAVING
    SUM(ATOTAL.HOURS_ABSENT) > 10
    OR SUM(case when year(Date) = 2010 then ABSENCE.HOURS_ABSENT else 0 end) > 3

编辑：

这没什么大不了的，但我讨厌重复条件，所以我们可以重构如下：

Select * From
(
    SELECT
        E.EMPID
        ,SUM(ABSENCE.HOURS_ABSENT) AS ABSENT_TOTAL
        ,SUM(case when year(Date) = 2010 then ABSENCE.HOURS_ABSENT else 0 end) AS ABSENT_YEAR

    FROM
        EMPLOYEE E

        INNER JOIN ABSENCE ON
            ABSENCE.EMPID = E.EMPID

    GROUP BY
        E.EMPID
    ) EmployeeAbsences
    Where ABSENT_TOTAL > 10 or ABSENT_YEAR > 3

这样，如果你改变你的案例条件，它只会在一个地方。

Answer 2

将不同的事物分开分组，加入组。

SELECT
  T.EMPID
  ,T.ABSENT_TOTAL
  ,Y.ABSENT_YEAR
FROM
    (
    SELECT
        E.EMPID
        ,SUM(A.HOURS_ABSENT) AS ABSENT_TOTAL
    FROM
        EMPLOYEE E
        INNER JOIN ABSENCE A ON A.EMPID = E.EMPID
    GROUP BY
        E.EMPID
    ) AS T
    INNER JOIN
    (
    SELECT
        E.EMPID
        ,SUM(A.HOURS_ABSENT) AS ABSENT_YEAR
    FROM
        EMPLOYEE E
        INNER JOIN ABSENCE A ON A.EMPID = E.EMPID
    WHERE
        A.DATE > '1/1/2010'
    GROUP BY
        E.EMPID
    ) AS Y
    ON T.EMPLID = Y.EMPLID
WHERE
    ABSENT_TOTAL > 10 OR ABSENT_YEAR > 3

此外，如果只有 SQL 关键字是大写字母而其余的不是，则可读性会增加。恕我直言。

Answer 3

SELECT E.EMPID , sum(ABSENT_TOTAL) , sum(ABSENT_YEAR)
FROM
(SELECT 
    E.EMPID 
    ,SUM(ATOTAL.HOURS_ABSENT) AS ABSENT_TOTAL 
    ,0 AS ABSENT_YEAR 

FROM 
    EMPLOYEE E 

    INNER JOIN ABSENCE ATOTAL ON 
        ATOTAL.EMPID = E.EMPID 
WHERE 
    AYEAR.DATE > '1/1/2010' 

GROUP BY 
    E.EMPID 

HAVING 
    SUM(ATOTAL.HOURS_ABSENT) > 10 

 UNION ALL

 SELECT 0    
    ,SUM(AYEAR.HOURS_ABSENT) 
 FROM 
    EMPLOYEE E    

       INNER JOIN ABSENCE AYEAR ON 
        AYEAR.EMPID = E.EMPID 

GROUP BY 
    E.EMPID 

HAVING  
    SUM(AYEAR.HOURS_ABSENT) > 3) a

    GROUP BY A.EMPID 

Answer 4

值得注意的是，您实际上不必在CASE 表达式中为ELSE 大小写提供0 值，如Jeremy's answer 所示。因为聚合函数不聚合 NULL 值，所以您可以将其留空并使用 CASE 表达式仅指定要在聚合中包含的值，例如

SELECT 
  e.empid,
  SUM(CASE WHEN <something> THEN atotal.hours_absent END) AS absent_total,
  SUM(CASE WHEN <something> THEN ayear.hours_absent END) AS absent_year
FROM ...