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SQL Union All

The purpose of the SQL UNION ALL command is also to combine the results of two queries together. The difference between UNION ALL and UNION is that, while UNION only selects distinct values, UNION ALL selects all values.

The syntax for UNION ALL is as follows:

[SQL Statement 1]
UNION ALL
[SQL Statement 2]

Let's use the same example as the previous section to illustrate the difference. Assume that we have the following two tables,

Table Store_Information
store_name Sales 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
Date Sales
Jan-07-1999 $250
Jan-10-1999 $535
Jan-11-1999 $320
Jan-12-1999 $750

and we want to find out all the dates where there is a sales transaction. To do so, we use the following SQL statement:

SELECT Date FROM Store_Information
UNION ALL
SELECT Date FROM Internet_Sales

Result:

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


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