What is the difference between Union and Union All?

UNION: only keeps unique records. UNION ALL: keeps all records, including duplicates

Union- It combines two more queries and removes the duplicates.

UnionAll- It combines two more queries and keeps the duplicates.

For example: TableA has 1,2,3 and Table B has 3,4,5
Union Result will be 1,2,3,4,5 (It removes the duplicate 3)
Union All Result will be 1,2,3,3,4,5 (It keeps the duplicate 3)

Which one will be faster?
Union All will be faster, as it does not remove the duplicates.

Navaneeth Krishnan6y

Union All return all rows from tables even duplicate also, however, Union exclude duplicate rows from tables.

6y

What is the difference between Union and Union All?

3 Answers