SQL Intermediate Lesson 6: UNION, INTERSECT and EXCEPT

📎 This article includes 2 downloadable practice files ↓

📘 SQL Intermediate Course · Lesson 6 of 10

Set operators stack the results of two queries with the same number of columns.

SELECT customer_id FROM orders WHERE product_id = 1
INTERSECT
SELECT customer_id FROM orders WHERE product_id = 3;

SELECT order_date AS day, 'Order' AS type, order_id FROM orders
UNION ALL
SELECT paid_on, 'Payment', order_id FROM payments
ORDER BY day, type;

Column names come from the first query; one ORDER BY at the very end sorts the combined result.

Common mistakes

• UNION when you meant UNION ALL: two genuine ₹499 payments on the same day collapse into one.
• Columns in a different order in the two queries: SQL matches by position, not by name.

Practice

Download shop2.db and this lesson’s exercise file below. Open the database in DB Browser for SQLite (free), paste each task into the Execute SQL tab and compare with the expected result printed under it. Answers are at the bottom of the file.