duplication check

[Anon]

Dear readers,

I've a Db of version 3.22.32.Can any one tell me how to get find the duplication entry from a column. Say table has a columnA with:
12
12
13
14
12
15
13
and so on.

Now how to get the duplicated entry and if found, then:-
1) how to get/print the repeated entry and
2) how to get only one entry out of repeated entries so that there is no duplication in the result.

And how the same purpose can be achieved if the numbers are in a file, insted of a Database.

Thanks.

[Anon]

For the database, use:

SELECT columnA, count(*) FROM table GROUP BY columnA