Sql server 2008 如何在SQL中选择每列最大值?
在SQL Server中,我有一个整数、日期时间和字符串的列表。比如说,Sql server 2008 如何在SQL中选择每列最大值?,sql-server-2008,loops,group-by,aggregate-functions,Sql Server 2008,Loops,Group By,Aggregate Functions,在SQL Server中,我有一个整数、日期时间和字符串的列表。比如说, number datetime string 6 2011-09-22 12:34:56 nameOne 6 2011-09-22 1:23:45 nameOne 6 2011-09-22 2:34:56 nameOne 5 2011-09-22 3:45:01 nameOne 5 2011-09-22 4:56:01
number datetime string
6 2011-09-22 12:34:56 nameOne
6 2011-09-22 1:23:45 nameOne
6 2011-09-22 2:34:56 nameOne
5 2011-09-22 3:45:01 nameOne
5 2011-09-22 4:56:01 nameOne
5 2011-09-22 5:01:23 nameOne
7 2011-09-21 12:34:56 nameTwo
7 2011-09-21 1:23:45 nameTwo
7 2011-09-21 2:34:56 nameTwo
4 2011-09-21 3:45:01 nameTwo
4 2011-09-21 4:56:01 nameTwo
4 2011-09-21 5:01:23 nameTwo
declare @max int
declare my_cursor cursor fast_forward for
select distinct string
from table
open my_cursor
fetch next from my_cursor into @string
while @@fetch_status = 0
begin
set @max = (select max(number) from table where string = @string)
select * from table where number = @max
fetch next from my_cursor into @string
end
close my_cursor
deallocate my_cursor
我想编写一个SQL语句,只输出每个字符串的最大行数。在这个例子中
number datetime string
6 2011-09-22 12:34:56 nameOne
6 2011-09-22 1:23:45 nameOne
6 2011-09-22 2:34:56 nameOne
7 2011-09-21 12:34:56 nameTwo
7 2011-09-21 1:23:45 nameTwo
7 2011-09-21 2:34:56 nameTwo
我知道我可以循环字符串列中的每个字符串,然后获取该字符串的最大值,然后选择与该最大值匹配的行。比如说,
number datetime string
6 2011-09-22 12:34:56 nameOne
6 2011-09-22 1:23:45 nameOne
6 2011-09-22 2:34:56 nameOne
5 2011-09-22 3:45:01 nameOne
5 2011-09-22 4:56:01 nameOne
5 2011-09-22 5:01:23 nameOne
7 2011-09-21 12:34:56 nameTwo
7 2011-09-21 1:23:45 nameTwo
7 2011-09-21 2:34:56 nameTwo
4 2011-09-21 3:45:01 nameTwo
4 2011-09-21 4:56:01 nameTwo
4 2011-09-21 5:01:23 nameTwo
declare @max int
declare my_cursor cursor fast_forward for
select distinct string
from table
open my_cursor
fetch next from my_cursor into @string
while @@fetch_status = 0
begin
set @max = (select max(number) from table where string = @string)
select * from table where number = @max
fetch next from my_cursor into @string
end
close my_cursor
deallocate my_cursor
但是,我想知道是否有一种方法可以在不使用循环的情况下完成此任务(例如,通过使用聚合函数和分组)