SQL UNION Operator – Unification of Sets with Example

By | 18. 1. 2020

UNION operator makes it possible to connect 2 results of query and remove all existing duplicities in them. In other words, operator actually performs DISTINCT in final unification of records.


FROM dbo.Table
WHERE Condition


FROM dbo.Table
WHERE Condition;

Syntax is same as in all Set operators. Result of unification is all records from both tables – If there is a column (or columns) with identical value in both tables, only unique value will be the result.

(!!!) UNION Operator performs unification and removes duplicities

UNION Example

Let’s have a table with a list of products


We will perform unification of 2 queries to demonstrate my point:

  • first query – records where Product Key (Primary key) is lower than 10
  • second query – records where Product Key (Primary key) is lower than 5


SELECT [ProductKey], [EnglishProductName]
FROM [AdventureWorksDW2014].[dbo].[DimProduct]
WHERE [ProductKey]<=10


SELECT [ProductKey], [EnglishProductName]
FROM [AdventureWorksDW2014].[dbo].[DimProduct]
WHERE [ProductKey]<=5;

Script result:

SQL UNION Výsledek

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Category: SQL Operators

About Jan Zedníček

My name is Jan Zedníček and I work as a freelancer. I have been working as a freelancer for many companies for more than 5 years. I used to work as a financial controller, analyst and manager at many different companies in field of banking and manufacturing. When I am not at work, I like playing volleyball, chess, doing a workout in the gym and I enjoy tasting of best quality rums. I am trying to summarize all my knowledge on this website not to forget them (because of the rum effect, you know =) and to put them forward to anyone. Don´t worry about asking for help or writing some comments.

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