What is the difference between SQL UNION and UNION ALL?

What is the difference between SQL UNION and UNION ALL?

SQL UNION combines the results of two or more SELECT statements, removing duplicates, while UNION ALL includes all results.

Can you give me an example of when to use UNION ALL?

Sure! Use UNION ALL when you want to combine results from multiple tables without filtering out duplicates, like merging sales data.

Are there performance differences between the two?

Yes, UNION ALL is generally faster than UNION because it doesn't check for duplicates, making it more efficient for large datasets.

What happens if the SELECT statements have different columns?

If the SELECT statements have different columns, SQL will throw an error. The number of columns and their data types must match.

Can I use UNION with other SQL clauses?

Yes, you can use UNION with other clauses like WHERE, ORDER BY, and GROUP BY to refine your results.