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SQL Server UNION Operator

In SQL Server, the UNION operator is used to combine the result-set of two or more SELECT statements.


Parameter explanation

expression1, expression2, ... expression_n: expressions specify the columns or calculations that you want to compare between the two SELECT statements.

tables: It specifies the tables that you want to retrieve records from. There must be at least one table listed in the FROM clause.

WHERE conditions: It is optional condition. It specifies the conditions that must be met for the records to be selected.

Image representation:

SQL union operator 1

Note: The covered blue area specifies the union data.

UNION operator with single expression



SQL union operator 2

UNION operator with multiple expressions


Let's use multiple expressions of each table. For example: id, name, salary.


SQL union operator 3

UNION ALL Operator

The UNION operator selects only distinct values by default. So, the UNION ALL operator is used to allow duplicate values also.



SQL union operator 4

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