MySQL JOINs Explained: INNER, LEFT, RIGHT and FULL

Real-world data lives in multiple tables — customers here, orders there. JOINs stitch them back together, and they are the most heavily tested SQL skill in analytics interviews.

Key Points

• INNER JOIN: only rows that match in both tables
• LEFT JOIN: all rows from the left table, matched rows (or NULLs) from the right
• RIGHT JOIN: mirror of LEFT JOIN — all rows from the right table
• FULL OUTER JOIN isn't native in MySQL — simulate with LEFT JOIN UNION RIGHT JOIN
• Always join on keys: ON orders.customer_id = customers.id
• Table aliases (customers c, orders o) keep multi-join queries readable