Sql Joins — Free Sql Tutorial

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

Sql Joins in Sql

JOINs combine data from two or more tables based on a related column. This is the heart of relational databases. Instead of storing all info in one table, we split data into related tables (normalization) and JOIN when needed.

INNER JOIN returns only matching rows from both tables. LEFT JOIN returns all rows from the left table + matched rows from right (NULL if no match). RIGHT JOIN is the opposite. FULL OUTER JOIN returns all rows from both tables.

The ON clause specifies which columns to join on — usually the primary key of one table matching the foreign key of another.

-- INNER JOIN (only matching rows)
SELECT a.col, b.col
FROM table_a a
INNER JOIN table_b b ON a.id = b.a_id;

-- LEFT JOIN (all from left, match from right)
SELECT a.col, b.col
FROM table_a a
LEFT JOIN table_b b ON a.id = b.a_id;

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