Write a SQL query to find duplicate records in the employee table.

To find duplicate records in the employee table, group by all columns and filter groups with count > 1. Example:

SELECT emp_id, first_name, last_name, hire_date, COUNT(*) AS dup_cnt

FROM employee

GROUP BY emp_id, first_name, last_name, hire_date

HAVING COUNT(*) > 1;

This returns the rows that appear more than once. If you want to see the duplicate rows themselves, you can join this result back to the original table. Complexity is O(n) with hashing or O(n log n) with sorting, depending on the DB engine. Ensure you have appropriate indexes on the columns used in the GROUP BY to improve performance.