为什么 CROSS APPLY 和 INNER JOIN returns 不同的结果

Question

为什么要交叉应用 return 额外的行。它的工作方式不应该类似于 INNER JOIN 吗？我期望的结果是

QuoteID  controlNo  etc            MaxQuoteID   COntrolNo
10101     1111     something15     10101        1111

示例数据：

-- create first example table
drop table if exists #test1
create table #test1 (QuoteID int, controlNo int, etc varchar(100))
insert into #test1 values 
(1111, 1111,'something1'),
(10101, 1111,'something15'),
(2222, 2222,'something2'),
(3333, 3333,'something3'),
(3333, 30303,'something35'),
(4444, 4444,'something4')
select * from #test1

--create second example table
drop table if exists #test2
create table #test2 (QuoteID int, ControlNo int)
insert into #test2 values 
(1111,1111),
(10101,1111)
select * from #test2

-- resutl query 1. This one works as expected
select * 
from #test1 t
inner join (select max(QuoteID) as MaxQuoteID, COntrolNo from #test2 group by ControlNo) tt ON t.QuoteID = tt.MaxQuoteID

-- But why this one doesnt work?
select * 
from #test1 t
cross apply 
(
-- subquery returns a single quoteid 10101, which is what I need
select max(QuoteID) as QuoteID
from #test2 tt
where tt.QuoteID = t.QuoteID
group by ControlNo
) a

Answer 1

两个查询不一样。

在查询 1 中，您希望 max(QuoteID) 按 controlNo

分组

在查询 2 中，每个 controlNo

得到 max(QuoteID)

如果你想使用 CROSS APPLY 等效，应该是

select  * 
from    #test1 t
        cross apply 
        (
            select  max(tt.QuoteID) as QuoteID, tt.controlNo
            from    #test2 tt
            group by tt.controlNo
            having  max(QuoteID) = t.QuoteID
        ) a

为什么 CROSS APPLY 和 INNER JOIN returns 不同的结果

Why CROSS APPLY and INNER JOIN returns different result

tsql

sql-server

join

cross-apply