SQL & DatabasesNot Started
SQL JOINs
Combine data from multiple tables with INNER, LEFT, RIGHT joins
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Partial Coverage
This skill is being actively expanded. You'll get real value from what's here, but it doesn't cover everything yet.
Available now:
- SELECT, WHERE, ORDER BY, LIMIT
- JOINs (INNER, LEFT, RIGHT)
- Aggregates & GROUP BY
- Indexes & Performance
Coming soon:
- Transactions & ACID
- Database Design & Normalization
- Window Functions
- Query Optimization with EXPLAIN
Explanation
JOINs combine rows from multiple tables based on a related column.
sql
SELECT users.name, orders.total
FROM users
INNER JOIN orders ON users.id = orders.user_id;Types:
- INNER JOIN — only rows with matches in BOTH tables
- LEFT JOIN — all rows from left table + matching from right (NULLs for no match)
- RIGHT JOIN — all rows from right + matching from left
- FULL OUTER JOIN — all rows from both tables
LEFT JOIN is the most commonly used because it keeps all records from your main table even when related data is missing.
Next in SQL & Databases
Aggregate Functions