Question

假设我有一个employee表，其中一列为DateOfJoining。我输入的数据为

现在，我想编写SQL查询来查找参加人数最大的月份。

Answer 1

您可以在下面尝试-使用汇总和TOP

select top 1 month(dateofjoining),count(*) as totaljoining
from tablename
where year(dateofjoining)=2019
group by month(dateofjoining)
order by 2 desc

Answer 2

使用Derived table和row_number()

下面的查询将为您提供每年最大参加人数的月份。

select cnt,mnth,yr
from
(select count(DateOfJoining)cnt,
        month(DateOfJoining)mnth,
        year(DateOfJoining)yr,
        row_number()over(partition by year(DateOfJoining) order by count(DateOfJoining)desc)srno
 from #employee
 group by month(DateOfJoining),year(DateOfJoining) 
)tbl
where srno = 1

输出

cnt         mnth        yr
----------- ----------- -----------
1           8           2010
3           12          2019

，如果要在2019年使用，则在where子句中添加条件yr ='2019'。

where srno = 1
and yr =2019

输出

cnt         mnth        yr
----------- ----------- -----------
3           12          2019

Answer 3

您既要最大又要最少-尽管我猜测您至少需要一名员工。

with e as (
      select year(dateofjoining) as yyyy,
             month(dateofjoining) as mm,
             count(*) as totaljoining
      from employee
      where dateofjoining >= '2019-01-01' and
            dateofjoining < '2020-01-01'
      group by year(dateofjoining), month(dateofjoining)
     )
select e.*
from ((select top (1) e.*
       from e
       order by totaljoining asc
      ) union all
      (select top (1) e.*
       from e
       order by totaljoining desc
      ) 
     ) e;

注意：

日期比较使用对日期的直接比较，而不是使用函数。这是最佳做法，因此优化程序可以使用索引。
您既要获得最小值，又要获得最大值，因此使用CTE，因此group by仅代表一次。
如果没有员工，这将不会返回几个月。
如果要联系，请使用top (1) with ties。

查找2019年分别有最高和最低新加入人数的月份

3 个答案: