What is the difference between UNION and UNION ALL?

SQL SELECT, filtering and sorting · Experienced

Model answer

UNION combines results and removes duplicates, which needs extra work. UNION ALL keeps all rows and is faster. Both need the same number of compatible columns. Use UNION ALL unless you need deduplication.

Learn this topic

SELECT, FROM and WHERE: Your First Queries in the course SQL for Beginners: Learn Databases Step by Step.

Sign in to add your own answer.

More questions

• How do you select specific columns and filter rows?
• How do you combine conditions in WHERE?
• What does LIKE do, and what are % and _?
• How do you sort and limit results?
• What does DISTINCT do?
• What is an alias?