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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).
The syntax of UNION in SQL is as follows:
[SQL Statement 1]
[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.
We use the following tables for our example.
To find all the dates where there is a sales transaction, we use the following SQL statement:
SELECT Txn_Date FROM Store_Information
SELECT Txn_Date FROM Internet_Sales;
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.