Stuck on a SQL problem for a databricks applications where I am trying to identify which unique values in one column are in two or more groups. For example:

```
COL_A  COL_B
 123     A
 234     B
 345     B
 123     B
 456     A
 567     C
 345     C
 345     A

```

The results I seek would tell me that unique value 123 was found in both groups A and B, and 345 was found in groups B, C, and A. Something like ...

```
123   A
123   B
345   B
345   C
345   A

```

or is there is a better way?