统计交叉相等两列元祖的次数 去掉重复

-- 统计交叉相等两列元祖的次数 去掉重复

if object_id('[tb]') is not null drop table [tb] 
go  
create table [tb]([num1] varchar(10),[num2] varchar(10)) 
insert [tb] 
select 'a','b' union all 
select 'b','c' union all 
select 'b','a' union all 
select 'c','b' union all 
select 'c','d' union all 


select * from tb 


select t.num1,t.num2,count(*)as 重复 
     from ( 
      select num1,num2 from tb 
      union all 
      select num2,num1 from tb     
     ) t 
     where t.num1<t.num2 
     group by t.num1,t.num2 


/* 

num1    num2 
a        b 
b        c 
b        a 
c        b 
c        d 

---------------------------- 

num1    num2    (重复) 
a         b         2 
b         c         2 
c         d         1 

*/