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移除书签| title | sidebar_label | description |
|---|---|---|
UNION keyword | UNION | UNION SQL keyword reference documentation. |
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 |
