Get duplicates values from values table

Create table
CREATE TABLE IF NOT EXISTS `emp1` (
`first_name` varchar(20) NOT NULL,
`last_name` varchar(20) NOT NULL
)

Insertion

INSERT INTO `emp1` (`first_name`, `last_name`) VALUES (‘roy’, ‘raj’), (‘joy’, ‘josh’);

SELECT `first_name`
FROM emp1
GROUP BY `first_name`
HAVING COUNT(*) = N

Change the HAVING condition to >=2
It outputs roy and joy are duplicates having more then one record wirh same value.

Change the HAVING condition to >1 to list non duplicate values, etc