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What is the difference between Union and Union All?

Cristopher Coronado

Cristopher Coronado
5y
1.8k
4
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    Navaneeth Krishnan

    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 Krishnan
    5y
    4
    Sam Khan
    Union All return all rows from tables even duplicate also, however, Union exclude duplicate rows from tables.
    Sam Khan
    5y
    1
    Nisha Regil
    UNION: only keeps unique records. UNION ALL: keeps all records, including duplicates
    Nisha Regil
    5y
    0
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