How to display duplicates in two columns?

Question

MySQL

You need to display a list of duplicates.
Those. There are two columns, you need to find identical values ​​in them.
Example:

Column1 Column2
123 235
768 178
127 758
556 556
184 185
997 997

Also, additionally
how to add to this find values ​​that are identical in characters, but in the first column or second contain spaces, unlike the other column? Is this done with a regex embedded in sql?