Question

我有字段A，B，C的以下数据：

我需要找到产生最大A值的B和C对，然后选择下一个最大值，使其不包含A或B。在上述数据中，第一次尝试选择1, 2，因为99是最大值。第二个过程排除了所有带有1或2的对，因此我们留下3 3，4 3和4 4，第二个最大值为4 4。该过程继续，结果是：

A  B  C
-- -- --
1  2  99
4  4  87
3  3  9

如何使用SQL执行此操作？

Answer 1

declare @a table (a int,b int,c int)
insert into @a values (1, 1, 90)
,(1, 2, 99)
,(1, 3, 75)
,(1, 3, 75)
,(2, 1, 60)
,(2, 2 ,54)
,(2, 3, 95)
,(3, 1, 85)
,(3, 2, 80)
,(3, 3, 9)
,(4, 1, 80)
,(4, 2, 85)
,(4, 3 ,86)
,(4, 4, 87);
Declare @rct int

Select top 1 *
into #tmp
from @a
Order by c desc

Select @rct=@@ROWCOUNT
While @rct>0
    begin
     Insert into #tmp
     Select Top 1 a.*
     from @a a
     Left Join #tmp on #tmp.A=a.A or #tmp.B=a.B or #tmp.b=a.A or #tmp.A=a.b
     Where #tmp.a is null and #tmp.b is null
     Order by C desc 
     Select @rct=@@ROWCOUNT
    end

Select * from #tmp
order by c desc
Drop table #tmp

有60万行，你可以试试这次尝试

declare @a table (a int,b int,c int)
insert into @a values (1, 1, 90)
,(1, 2, 99)
,(1, 3, 75)
,(1, 3, 75)
,(2, 1, 60)
,(2, 2 ,54)
,(2, 3, 95)
,(3, 1, 85)
,(3, 2, 80)
,(3, 3, 9)
,(4, 1, 80)
,(4, 2, 85)
,(4, 3 ,86)
,(4, 4, 87);
Declare @rct int

Select a,b,c 
into #work
from @a   --  your big table
CREATE NONCLUSTERED INDEX [i_a] ON #work (a)
CREATE NONCLUSTERED INDEX [i_b] ON #work (b)
CREATE NONCLUSTERED INDEX [i_c] ON #work (c)

Select top 1 *
into #tmp
from #work
Order by c desc

Select * 
into #final
from #tmp

Delete #work 
from #tmp
where #work.a=#tmp.a or #work.b=#tmp.a or #work.a=#tmp.b or #work.b=#tmp.b

While (Select COUNT(*) from #work) >0
    begin
    delete from #tmp

    insert into #tmp
    Select top 1 *  
    from #work
    Order by c desc

    insert into #final
    Select *    
    from #tmp

    Delete #work 
    from #tmp
    where #work.a=#tmp.a or #work.b=#tmp.a or #work.a=#tmp.b or #work.b=#tmp.b
    end 

drop table #work
drop table #tmp
Select * from #final
drop table #final

递归选择唯一的最大值

1 个答案: