Problem with "Find Duplicates" using subquery

[Michael Berkowitz]

Hello,

I'm using Version 4.1.10-Debian_1.

Here's the query I'm running:

select * from Donations where Donation_id in
(SELECT Donation_id FROM Donations group by date, amt, donor having count(*) > 1)

The idea is to find all the Donations records that have the same date, amt and donor as one-or-more other records -- in short, a "Find Duplicates" query.

The logic of the query is to first find the primary keys ('Donation_id') of these records in a subquery, then retrieve all the other fields for those records. The subquery works fine when I run it by itself.

The server accepts the syntax of the full query and runs it, but it just spins its wheels and never returns; I mean, I let it run long enough that if it were going to return, it would have. Doing a "show processlist" shows the state of the process running this query as "Copying to tmp table".

I'd appreciate any insight anyone can give me.

TIA

Michael