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_NameSalesTxn_Date
Los Angeles1500Jan-05-1999
San Diego250Jan-07-1999
Los Angeles300Jan-08-1999
Boston700Jan-08-1999

Table Internet_Sales

Txn_DateSales
Jan-07-1999250
Jan-10-1999535
Jan-11-1999320
Jan-12-1999750

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




Copyright © 2017   1keydata.com   All Rights Reserved     Privacy Policy     About   Contact