I have the following SQL table which shows case number and their value, the case number always appear 2 cases in a group, I want to count how many the combinations with same case number appearing in the table. Be ware the order could be different, see case A and C, both of them should be count as the same combination. 

```
case  value

A     1992

A     1956

B     2000

B     2001

C     1956

C     1992

```

**The goal is to get the total number of each combination, so the output format doesn't matter. One of expected result:**

```
Seq  value   frequency

1    1992    2

1    1956    2

2    2000    1

2    2001    1

```

**What about if there are 3 cases as a combination?**