SQL UNION ALL

The purpose of the SQL UNION ALL command is to combine the results of two queries together without removing any duplicates.

Syntax

The syntax for UNION ALL is as follows:

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

Example

We use the following tables for our example.

Table Store_Information

Table Internet_Sales

To find out all the dates where there is a sales transaction at a store as well as all the dates where there is a sale over the internet, we use the following SQL statement:

Result:

UNION vs UNION ALL

UNION and UNION ALL both combine the results of two SQL queries. The difference is that, while UNION only returns distinct values, UNION ALL selects all values. If we use UNION in the above example,

the result becomes,

Notice that while the UNION ALL query returns "Jan-07-1999" and "Jan-08-1999" twice, the UNION query returns each value only once.