Combining Queries - MariaDB Crash Course - page 139

▼ Analysis
The first SELECT retrieves all products with a price of no more than 5 . The
second SELECT uses IN to find all products made by vendors 1001 and 1002 .
To combine these two statements, do the following:
▼ Input
SELECT vend_id, prod_id, prod_price
FROM products
WHERE prod_price <= 5
UNION
SELECT vend_id, prod_id, prod_price
FROM products
WHERE vend_id IN (1001,1002);
▼ Output
+---------+---------+------------+
| vend_id | prod_id | prod_price |
+---------+---------+------------+
| 1003 | FC | 2.50 |
| 1002 | FU1 | 3.42 |
| 1003 | SLING | 4.49 |
| 1003 | TNT1 | 2.50 |
| 1001 | ANV01 | 5.99 |
| 1001 | ANV02 | 9.99 |
| 1001 | ANV03 | 14.99 |
| 1002 | OL1 | 8.99 |
+---------+---------+------------+
▼ Analysis
The preceding statements are made up of both of the previous SELECT state-
ments separated by the UNION keyword. UNION instructs MariaDB to execute
both SELECT statements and combine the output into a single query result set.
As a point of reference, here is the same query using multiple WHERE clauses
instead of a UNION :
▼ Input
SELECT vend_id, prod_id, prod_price
FROM products
WHERE prod_price <= 5
OR vend_id IN (1001,1002);