选择1条记录，其中两条记录在不同列中具有相同的值

Question

我有一个包含两列的表。

的前两行的列值是反转的，我将如何选择适合每一个地方一个STATION_1_I等于另一个记录STATION_2_I及其STATION_2_I等于STATION_1_I例如一个记录

。

Answer 1

INTERSECT将删除重复你

select "station_1_I", "station_2_I" from mytable 
intersect 
select "station_2_I", "station_1_I" from mytable 
      where "station_2_I" < "station_1_I" 

SQL Fiddle

Answer 2

select a,b from 
(
select 
(case when a<b then a else b end) as a, 
(case when a>b then a else b end) as b 
from (
select station_1_I as a, station_2_I as b from MyTable 
union all 
select station_2_I, station_1_I from MyTable 
) having count(*)=2 group by a,b 
) group by a,b