Finding duplicate values in MySQL

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 duplicates?

Answer

Do a SELECT with a GROUP BY clause. Let's say name is the column you want to find duplicates in:

SELECT name, COUNT(*) c FROM table GROUP BY name HAVING c > 1;

This will return a result with the name value in the first column, and a count of how many times that value appears in the second.