Background Back when I got my GL-AR150 mini router, I was blown away by the powerful capabilities of this $25 OpenWRT router,...
Check if column in MySQL table has duplicate valuesStanislav Khromov
So you have a column that is not UNIQUE, but you’d still like to check if there is duplicate values in it.
If your column name is my_column in table my_table, the query is:
SELECT my_column, COUNT(*) as count FROM my_table GROUP BY my_column HAVING COUNT(*) > 1
This will return all records that have duplicate my_column content, as well as how many times this content occurs in the database.