Sql Self Join — Free Sql Tutorial

TL;DR: Learn Sql Self Join in Sql with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Sql Self Join in Sql

A self-join joins a table to a copy of itself, useful for finding relationships within the same table: employee-manager hierarchy, product comparisons, duplicate detection.

Use table aliases (a, b) to distinguish the two copies: FROM employees e1 JOIN employees e2 ON e1.manager_id = e2.emp_id.

Common uses: "find all employees and their managers", "find products in the same category with price differences", "find pairs of employees in the same department".

-- Employee and manager (both from employees table)
SELECT e.name AS employee, m.name AS manager
FROM employees e
LEFT JOIN employees m ON e.manager_id = m.emp_id;

-- Find pairs of friends in the same city
SELECT f1.name, f2.name, f1.city
FROM friends f1
JOIN friends f2 ON f1.city = f2.city AND f1.

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