SQL：如何创建结果如下所示

Question

I facing issue with the below case:

I/P Table:

Column_1  Column_2
A             A 
B             B 
C             C
D             D

Cross Join will give me the below result

Actual O/P Value:
AA
AB--This combinati

on is Repeated
    AC
    AD

BA--This combination is Repeated
BB
BC
BD

CA
CB
CC
CD

DA
DB
DC
DD

Expected OP:

AA
AB
AC
AD

BB
BC
BD

CC
CD

DD

I dont want the combinations to be repeated: Like AB and BA.

Answer 1

添加一个额外条件，要求第二个值大于或等于第一个值：

.... WHERE (Column_2 >= Column_1)

Answer 2

select distinct least(column_1, column_2), greatest(column_1, column_2)
from ip_table 
   cross join ip_table
order by 1