🔗 JoinsintermediateCommonly used

How to use INNER JOIN in SQL

Return only rows that have matching records in both tables.

Table schema used in examples— users and orders tables

CREATE TABLE users (
  id      INTEGER PRIMARY KEY,
  name    TEXT,
  email   TEXT,
  country TEXT
);

CREATE TABLE orders (
  id         INTEGER PRIMARY KEY,
  user_id    INTEGER REFERENCES users(id),
  total      DECIMAL,
  status     TEXT,
  created_at TIMESTAMP
);

Basic INNER JOINAll databases

SELECT
  u.name,
  u.email,
  o.total,
  o.status
FROM users u
INNER JOIN orders o ON u.id = o.user_id;

Returns only users who have at least one order. Users with no orders are excluded.

When to use: When you only want rows that have a match in both tables.

JOIN with WHERE filterAll databases

SELECT
  u.name,
  o.total,
  o.created_at
FROM users u
INNER JOIN orders o ON u.id = o.user_id
WHERE o.total > 100
  AND o.status = 'completed';

Combines JOIN with filtering. The WHERE clause applies after the join.

JOIN with ORDER BY and LIMITAll databases

SELECT
  u.name,
  SUM(o.total) AS total_spent
FROM users u
INNER JOIN orders o ON u.id = o.user_id
GROUP BY u.id, u.name
ORDER BY total_spent DESC
LIMIT 10;

Top 10 customers by total spend — joins users and orders, aggregates, and limits results.

JOIN three tablesAll databases

SELECT
  u.name,
  o.total,
  p.name AS product_name
FROM users u
INNER JOIN orders o       ON u.id = o.user_id
INNER JOIN order_items oi ON o.id = oi.order_id
INNER JOIN products p     ON oi.product_id = p.id;

Chain multiple JOINs to connect three or more tables.

Common Mistakes

→Forgetting the ON clause — results in a cartesian product (every row × every row)
→Not using table aliases — queries become hard to read with long table names
→INNER JOIN vs LEFT JOIN — INNER excludes non-matching rows, LEFT keeps them

Common Mistakes

Related Topics