刪除重複2000

Question

我有表：

number city1 city2 mentions 
1 a b 5 
1 b a 5 
1 c d 2 
1 d c 2 

我需要的是刪除重複的記錄，如A，B等於B，A變成了：

number city1 city2 mentions 
1 a b 5 
1 c d 2 

我的任何線索？

感謝之前:)

Answer 1

想要這樣嗎？

delete from table t1 
where exists (
    select * 
    from table t2 
    where 
    t2.number = t1.number and 
    t2.city1 = t1.city2 and 
    t2.city2 = t1.city1 and 
    t2.mentions = t1.mentions and 
    t2.city1 < t2.city2 
)