MYSQL SELECT
SELECT with DISTINCT
The DISTINCT clause after SELECT eliminates duplicate rows from the result set.
CREATE TABLE `car`
( `car_id` INT UNSIGNED NOT NULL PRIMARY KEY,
`name` VARCHAR(20),
`price` DECIMAL(8,2)
);
INSERT INTO CAR (`car_id`, `name`, `price`) VALUES (1, 'Audi A1', '20000');
INSERT INTO CAR (`car_id`, `name`, `price`) VALUES (2, 'Audi A1', '15000');
INSERT INTO CAR (`car_id`, `name`, `price`) VALUES (3, 'Audi A2', '40000');
INSERT INTO CAR (`car_id`, `name`, `price`) VALUES (4, 'Audi A2', '40000');
SELECT DISTINCT `name`, `price` FROM CAR;
+---------+----------+
| name | price |
+---------+----------+
| Audi A1 | 20000.00 |
| Audi A1 | 15000.00 |
| Audi A2 | 40000.00 |
+---------+----------+DISTINCT works across all columns to deliver the results, not individual columns. The latter is often a misconception of new SQL developers. In short, it is the distinctness at the row-level of the result set that matters, not distinctness at the column-level. To visualize this, look at "Audi A1" in the above result set.
For later versions of MySQL, DISTINCT has implications with its use alongside ORDER BY. The setting for ONLY_FULL_GROUP_BY comes into play as seen in the following MySQL Manual Page entitled MySQL Handling of GROUP BY.