我想写一个这样的查询:
SELECT o.OrderId, MAX(o.NegotiatedPrice, o.SuggestedPrice)
FROM Order o
但这不是MAX函数的工作原理,对吧?它是一个聚合函数,因此它需要一个参数,然后返回所有行的MAX。
有人知道我的方法吗?
我想写一个这样的查询:
SELECT o.OrderId, MAX(o.NegotiatedPrice, o.SuggestedPrice)
FROM Order o
但这不是MAX函数的工作原理,对吧?它是一个聚合函数,因此它需要一个参数,然后返回所有行的MAX。
有人知道我的方法吗?
当前回答
如果你使用的是SQL Server 2008(或更高版本),那么这是更好的解决方案:
SELECT o.OrderId,
(SELECT MAX(Price)
FROM (VALUES (o.NegotiatedPrice),(o.SuggestedPrice)) AS AllPrices(Price))
FROM Order o
所有的信用和投票都应该去Sven对一个相关问题的答案,“多列的SQL MAX ?” 我说这是“最佳答案”,因为:
It doesn't require complicating your code with UNION's, PIVOT's, UNPIVOT's, UDF's, and crazy-long CASE statments. It isn't plagued with the problem of handling nulls, it handles them just fine. It's easy to swap out the "MAX" with "MIN", "AVG", or "SUM". You can use any aggregate function to find the aggregate over many different columns. You're not limited to the names I used (i.e. "AllPrices" and "Price"). You can pick your own names to make it easier to read and understand for the next guy. You can find multiple aggregates using SQL Server 2008's derived_tables like so: SELECT MAX(a), MAX(b) FROM (VALUES (1, 2), (3, 4), (5, 6), (7, 8), (9, 10) ) AS MyTable(a, b)
其他回答
我会使用kcrumley提供的解决方案 只需稍微修改它以处理null
create function dbo.HigherArgumentOrNull(@val1 int, @val2 int)
returns int
as
begin
if @val1 >= @val2
return @val1
if @val1 < @val2
return @val2
return NULL
end
编辑 在Mark的评论后修改。正如他在3值逻辑x > NULL或x < NULL应该总是返回NULL。换句话说,未知的结果。
哎呀,我刚刚发布了一个关于这个问题的恶搞帖…
答案是,没有像Oracle's Greatest这样的内置函数,但是您可以通过UDF为两个列实现类似的结果,注意,sql_variant的使用在这里非常重要。
create table #t (a int, b int)
insert #t
select 1,2 union all
select 3,4 union all
select 5,2
-- option 1 - A case statement
select case when a > b then a else b end
from #t
-- option 2 - A union statement
select a from #t where a >= b
union all
select b from #t where b > a
-- option 3 - A udf
create function dbo.GREATEST
(
@a as sql_variant,
@b as sql_variant
)
returns sql_variant
begin
declare @max sql_variant
if @a is null or @b is null return null
if @b > @a return @b
return @a
end
select dbo.GREATEST(a,b)
from #t
克里斯汀
下面是我的回答:
create table #t (id int IDENTITY(1,1), a int, b int)
insert #t
select 1,2 union all
select 3,4 union all
select 5,2
select id, max(val)
from #t
unpivot (val for col in (a, b)) as unpvt
group by id
其实很简单:
CREATE FUNCTION InlineMax
(
@p1 sql_variant,
@p2 sql_variant
) RETURNS sql_variant
AS
BEGIN
RETURN CASE
WHEN @p1 IS NULL AND @p2 IS NOT NULL THEN @p2
WHEN @p2 IS NULL AND @p1 IS NOT NULL THEN @p1
WHEN @p1 > @p2 THEN @p1
ELSE @p2 END
END;
我不这么想。我那天想要这个。我最接近的说法是:
SELECT
o.OrderId,
CASE WHEN o.NegotiatedPrice > o.SuggestedPrice THEN o.NegotiatedPrice
ELSE o.SuggestedPrice
END
FROM Order o
对于SQL Server 2012:
SELECT
o.OrderId,
IIF( o.NegotiatedPrice >= o.SuggestedPrice,
o.NegotiatedPrice,
ISNULL(o.SuggestedPrice, o.NegiatedPrice)
)
FROM
Order o