Data duplication happens because of many reasons. Finding duplicate values is one of the important tasks that you must deal with when working with the databases.

In this tutorial, you will learn how to find duplicate values of one or more columns in MySQL.

Find duplicate values in one column

SELECT 
    col, 
    COUNT(col)
FROM
    table_name
GROUP BY col
HAVING COUNT(col) > 1;

Find duplicate values in multiple columns

SELECT 
    col1, COUNT(col1),
    col2, COUNT(col2),
    ...
 
FROM
    table_name
GROUP BY 
    col1, 
    col2, ...
HAVING 
       (COUNT(col1) > 1) AND 
       (COUNT(col2) > 1) AND 
       ...