MySQL - UNION Keyword

You can use UNION if you want to select rows one after the other from several tables or several sets of rows from a single table all as a single result set.

UNION is available as of MySQL 4.0. This section illustrates how to use it.

Suppose you have two tables that list prospective and actual customers, a third that lists vendors from whom you purchase supplies, and you want to create a single mailing list by merging names and addresses from all three tables. UNION provides a way to do this. Assume the three tables have the following contents −

mysql> SELECT * FROM prospect;
+---------+-------+------------------------+
|  fname  | lname |          addr          |
+---------+-------+------------------------+
| Peter   | Jones | 482 Rush St., Apt. 402 |
| Bernice | Smith |     916 Maple Dr.      |
+---------+-------+------------------------+
mysql> SELECT * FROM customer;
+-----------+------------+---------------------+
| last_name | first_name |       address       |
+-----------+------------+---------------------+
| Peterson  |   Grace    | 16055 Seminole Ave. |
|   Smith   |  Bernice   |    916 Maple Dr.    |
|   Brown   |   Walter   |    8602 1st St.     |
+-----------+------------+---------------------+
mysql> SELECT * FROM vendor;
+-------------------+---------------------+
|      company      |        street       |
+-------------------+---------------------+
| ReddyParts, Inc.  | 38 Industrial Blvd. |
| Parts-to-go, Ltd. | 213B Commerce Park. |
+-------------------+---------------------+

It does not matter if all the three tables have different column names. The following query illustrates how to select names and addresses from the three tables all at once −

mysql> SELECT fname, lname, addr FROM prospect
-> UNION
-> SELECT first_name, last_name, address FROM customer
-> UNION
-> SELECT company, '', street FROM vendor;
+-------------------+----------+------------------------+
|       fname       |   lname  |          addr          |
+-------------------+----------+------------------------+
|       Peter       |   Jones  | 482 Rush St., Apt. 402 |
|      Bernice      |   Smith  |     916 Maple Dr.      |
|       Grace       | Peterson |   16055 Seminole Ave.  |
|      Walter       |   Brown  |     8602 1st St.       |
| ReddyParts, Inc.  |          |   38 Industrial Blvd.  |
| Parts-to-go, Ltd. |          |   213B Commerce Park.  |
+-------------------+----------+------------------------+

If you want to select all records, including duplicates, follow the first UNION keyword with ALL −

mysql> SELECT fname, lname, addr FROM prospect
-> UNION ALL
-> SELECT first_name, last_name, address FROM customer
-> UNION
-> SELECT company, '', street FROM vendor;
+-------------------+----------+------------------------+
|       fname       |   lname  |          addr          |
+-------------------+----------+------------------------+
|       Peter       |   Jones  | 482 Rush St., Apt. 402 |
|      Bernice      |   Smith  |     916 Maple Dr.      |
|       Grace       | Peterson |   16055 Seminole Ave.  |
|      Bernice      |   Smith  |     916 Maple Dr.      |
|      Walter       |   Brown  |     8602 1st St.       |
| ReddyParts, Inc.  |          |   38 Industrial Blvd.  |
| Parts-to-go, Ltd. |          |   213B Commerce Park.  |
+-------------------+----------+------------------------+