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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 at a store as well as all the dates where there is a sale over the internet. 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 |
SQL INTERSECT >>
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