我想编写一个T-SQL查询,它不仅返回最大值,还返回具有最大值的行数.必须有比我想出的更好的方法
--wrong way
select LibraryBranchId, max(daysCheckedOut), count(daysCheckedOut)
from books group by LibraryBranchId
LibraryBranchId Expr1 Expr2
----------------------------------
1 100 398503 (WRONG!)
2 75 94303 (WRONG!)
3 120 103950 (WRONG!)
我可以通过INNER JOINing子查询来正确地做到这一点,但这看起来很浪费
--right way, but seems WAY too long
select LibraryBranchId,max(daysCheckedOut),count(daysCheckedOut)
from books inner join
( select LibraryBranchId, max(daysCheckedOut) as maxDaysCheckedOut
from books group by LibraryBranchId ) as maxbooks
on books.LibraryBranchId=maxbooks.LibraryBranchId
where daysCheckedOut=maxDaysCheckedOut
group by LibraryBranchId
LibraryBranchId Expr1 Expr2
----------------------------------
1 100 17 (RIGHT!)
2 75 11 (RIGHT!)
3 120 2 (RIGHT!)
那么有一种方法就像查询#1一样简单,但是在查询#2中返回正确的结果吗?
MS SQL Server 2000
编辑:我在第一次尝试输入时错过了两个重要的GROUP BY,我添加了它们
编辑:假装Cade Roux编写的版本是我写的
最佳答案 我认为这是对的:
SELECT maxbooks.LibraryBranchId, maxbooks.maxDaysCheckedOut, count(*)
FROM books
INNER JOIN (
SELECT LibraryBranchId, max(daysCheckedOut) AS maxDaysCheckedOut
FROM books
GROUP BY LibraryBranchId
) AS maxbooks
ON books.LibraryBranchId = maxbooks.LibraryBranchId
AND books.daysCheckedOut = maxbooks.maxDaysCheckedOut
GROUP BY maxbooks.LibraryBranchId, maxbooks.maxDaysCheckedOut
我不认为有一种更简单的方法 – 从概念上讲,它是两组的交集.关于分支的一组元组和满足该分支的一组tupes.