Question

我在MySQL中有两个表：

emp_detail
----------------------------------------------------------------------
emp_number(int)| emp_id(int) | emp_name(varchar) | joined_date (date)
----------------------------------------------------------------------

和

----------------------------------------------------------------------
emp_termination
----------------------------------------------------------------------
emp_number(int)foreign key| termination_reason(varchar) | termination_date (date)
----------------------------------------------------------------------

我想要每年的月度记录，包括每个月离开或加入公司的员工人数：

-----------------------
month | joined | left 
-----------------------

Answer 1

使用UNION ALL加入并将员工分成两行，然后按月合并以离开并加入一行。

SELECT year, month, SUM(joined), SUM(left)
FROM
    (SELECT YEAR(ed.joined_date) AS year, MONTH(ed.joined_date) AS month, COUNT(MONTH(ed.joined_date)) AS joined, 0 AS left
    FROM emp_detail AS ed
    GROUP BY YEAR(ed.joined_date), MONTH(ed.joined_date) 
    UNION ALL
    SELECT YEAR(ed.termination_date) AS year, MONTH(ed.termination_date) AS month, COUNT(MONTH(et.termination_date)) AS left, 0 AS joined
    FROM emp_termination AS et
    GROUP BY YEAR(ed.termination_date), MONTH(et.termination_date)) AS my_table
GROUP BY year, month

Answer 2

试试这个..

select table1.monthname, table1.Joined, table2.LeftCop from 
(
select  year(joined_date) year 
        , MONTHNAME(STR_TO_DATE( month(joined_date) , '%m')) as monthname
        ,count(*) as Joined 
        ,0 as LeftCop 
        from emp_detail
  group by  month(joined_date) , year(joined_date) 

) Table1

join 

(
select  year(termination_date) year 
        , MONTHNAME(STR_TO_DATE( month(termination_date) , '%m')) as monthname
        ,0 as Joined 
        ,count(*) as LeftCop  
        from emp_termination
  group by  month(termination_date) , year(termination_date) 
) table2 

on table1.year = table2.year and table1.monthname = table2.monthname

请帮我解决这个问题

2 个答案: