Question

我对单个表上的单个字段有2个查询，我想加入单个查询...

查询1：

SELECT completed_by_id AS WHO
    , COUNT (activity_id) AS CALLS
FROM table1
WHERE activity_id = 'CALL'
    AND YEAR(completed_date) = YEAR(GETDATE())
    AND MONTH(completed_date) = MONTH(GETDATE())
GROUP BY completed_by_id

返回：

WHO        *    CALLS
Joe Sales  *    5
Jane Sales *    8

查询2：

SELECT completed_by_id AS WHO
    , COUNT (activity_id) AS VISITS
FROM table1
WHERE activity_id = 'VISIT'
    AND YEAR(completed_date) = YEAR(GETDATE())
    AND MONTH(completed_date) = MONTH(GETDATE())
GROUP BY completed_by_id

返回：

WHO        *    VISITS
Joe Sales  *    2
Jane Sales *    3

这两种方法都可以正常工作，但我希望有一个返回类似的查询：

WHO          *   CALLS    *   VISITS  
Joe Sales    *     5      *    2
Jane Sales   *     8      *    3

我知道我需要自我加入，但我不确定如何编写查询。

Answer 1

这可以通过在COUNT中使用CASE语句来完成。 COUNT只有在非空时递增，因此当CASE不是您要查找的内容时，可以让CASE返回NULL，或者您可以使用SUM代替并返回1/0。 / p>

SELECT
    completed_by_id AS WHO, 
    COUNT(CASE WHEN (activity_id='CALL' THEN 1 END)) AS CALLS,
    COUNT(CASE WHEN (activity_id='VISIT' THEN 1 END)) AS VISITS
FROM table1
WHERE 
    activity_id IN ('CALL','VISIT') -- This is optional, but it could help efficiency a bit
    AND YEAR(completed_date) = YEAR(GETDATE()) AND 
    MONTH(completed_date) = MONTH(GETDATE())
GROUP BY completed_by_id

Answer 2

    SELECT completed_by_id AS WHO
    , sum(case when activity_id= 'CALL' then 1 else 0 end) AS CALLS
    , sum(case when activity_id= 'visits' then 1 else 0 end) AS VISITS
FROM table1
WHERE activity_id in  ('CALL','visits')
    AND YEAR(completed_date) = YEAR(GETDATE())
    AND MONTH(completed_date) = MONTH(GETDATE())
GROUP BY completed_by_id

SQL自带连接与相同字段上的计数功能不同的条款

2 个答案: