UNION keyword
Overview
UNION is used to combine the results of two or more SELECT statements. To
work properly:
- Each select statement should return the same number of column
- Each column should have the same type
- Columns should be in the same order
Syntax
UNIONwill return distinct results.UNION ALLwill return all results including duplicates.
Examples
Let's assume the following two tables listA
| Description | ID |
|---|---|
| Red Pen | 1 |
| Blue Pen | 2 |
| Green Pen | 3 |
listB
| Description | ID |
|---|---|
| Pink Pen | 1 |
| Black Pen | 2 |
| Green Pen | 3 |
liastA UNION listB
will return
| Description | ID |
|---|---|
| Red Pen | 1 |
| Blue Pen | 2 |
| Green Pen | 3 |
| Pink Pen | 1 |
| Black Pen | 2 |
liastA UNION ALL listB
will return
| Description | ID |
|---|---|
| Red Pen | 1 |
| Blue Pen | 2 |
| Green Pen | 3 |
| Pink Pen | 1 |
| Black Pen | 2 |
| Green Pen | 3 |