Relational SQL: INNER & LEFT Joins

📄 MySQLLesson 6Intermediate

Relational databases avoid duplicate data by linking tables. Joins query connected records by matching matching keys across distinct files.

1 Joining Tables

SQL — JOIN Examples

# INNER JOIN: Matches records that exist in BOTH tables
SELECT posts.id, posts.title, users.username
FROM posts
INNER JOIN users ON posts.user_id = users.id;

# LEFT JOIN: Returns ALL left-table records, plus matching right-table records (null if no match)
SELECT users.username, posts.title
FROM users
LEFT JOIN posts ON users.id = posts.user_id;

2 Code Challenge

Challenge: Write a query connecting an orders table to a customers table using an inner join. Retrieve order date, order total, and customer email address fields.