Finding duplicate values in MySQL

Question

I have a table with a varchar column, and I would like to find all the records that have duplicate values in this column. What is the best query I can use to find the duplic

Answer 1

Assuming your table is named TableABC and the column which you want is Col and the primary key to T1 is Key.

SELECT a.Key, b.Key, a.Col 
FROM TableABC a, TableABC b
WHERE a.Col = b.Col 
AND a.Key <> b.Key

The advantage of this approach over the above answer is it gives the Key.