SQL > Advanced SQL > Union

The purpose of the SQL UNION query is to combine the results of two queries together while removing duplicates. In other words, when using UNION, only unique values are returned (similar to SELECT DISTINCT).

Syntax

The syntax of UNION in SQL is as follows:

[SQL Statement 1]
UNION
[SQL Statement 2];

The columns selected in [SQL Statement 1] and [SQL Statement 2] need to be of the same data type for UNION to work.

Example

We use the following tables for our example.

Table Store_Information

 Store_Name  Sales  Txn_Date 
 Los Angeles  1500  Jan-05-1999 
 San Diego  250  Jan-07-1999 
 Los Angeles  300  Jan-08-1999 
 Boston  700  Jan-08-1999 

Table Internet_Sales

 Txn_Date  Sales 
 Jan-07-1999  250 
 Jan-10-1999  535 
 Jan-11-1999  320 
 Jan-12-1999  750 

To find all the dates where there is a sales transaction, we use the following SQL statement:

SELECT Txn_Date FROM Store_Information
UNION
SELECT Txn_Date FROM Internet_Sales;

Result:

Txn_Date
Jan-05-1999
Jan-07-1999
Jan-08-1999
Jan-10-1999
Jan-11-1999
Jan-12-1999

Please note that if we type "SELECT DISTINCT Txn_Date" for either or both of the SQL statement, we will get the same result set.

Next: SQL UNION ALL

This page was last updated on May 23, 2022.




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