Delete Duplicate Emails

Problem

Schema: Person(id INT, email VARCHAR) with id as PK. Delete duplicate rows so each email is kept exactly once — the row with the smallest id per email survives.

Constraints

• Don't change id of the surviving rows.

Approach — Core Patterns

This is a Core Patterns problem. The idea: pick the data structure best matched to the constraints and solve it in one clean pass. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: see the walkthrough below.

Solution code

SQL

DELETE p1
FROM Person p1
JOIN Person p2 ON p2.email = p1.email AND p2.id < p1.id;

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.