SQL · Pattern 11 — Interview SQL Patterns
Remove Duplicates
Deletes duplicate rows while keeping one record.
Source data — Pattern 11: Interview SQL Patterns
All queries run against the shared employees table (see schema.sql). Topics 71 and 72 introduce an orders table to solve consecutive records and gaps-and-islands problems. Topics 73 and 74 introduce a monthly_sales table to demonstrate PIVOT and UNPIVOT operations.
What it does
Deletes duplicate rows while keeping one record.
Problem
Delete duplicate employee records.
DELETE FROM employees
WHERE employee_id NOT IN (
SELECT MIN(employee_id)
FROM employees
GROUP BY email
);
Result
