MySQL - GROUP BY clause recursively? - mysql

Question

Under MySQL I can not group the three separate data columns via GROUP BY clause.
This sample contains four brands, each brand has 2 models and 4 versions of engines. I need to extract 4 vehicles the brand, the model and version of engines is different. A truly unique result in the 3 columns.
----------+--------+----------+
Brand | Model | Version |
----------+--------+----------+
Renault | Clio | Essence |
Citroen | C4 | GPL |
Ford | Fiesta | Gazole |
Peugeot | 206 | Electric |
----------+--------+----------+
This works 8/10.
SELECT brand, model, version
FROM cars WHERE version = (SELECT version FROM cars GROUP BY version ORDER BY RAND() LIMIT 1)
GROUP BY brand
An example of the table
CREATE TABLE IF NOT EXISTS `cars` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`brand` varchar(255) NOT NULL,
`model` varchar(255) NOT NULL,
`version` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=33 DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci ROW_FORMAT=COMPRESSED;
INSERT INTO `cars` (`id`, `brand`, `model`, `version`) VALUES
(1, 'Renault', 'Clio ', 'Essence'),
(2, 'Renault', 'Clio ', 'Gazole'),
(3, 'Renault', 'Clio ', 'GPL'),
(4, 'Renault', 'Clio ', 'Electric'),
(5, 'Renault', 'Modus', 'Essence'),
(6, 'Renault', 'Modus', 'Gazole'),
(7, 'Renault', 'Modus', 'GPL'),
(8, 'Renault', 'Modus', 'Electric'),
(9, 'Peugeot', '307', 'Essence'),
(10, 'Peugeot', '307', 'Gazole'),
(11, 'Peugeot', '307', 'GPL'),
(12, 'Peugeot', '307', 'Electric'),
(13, 'Peugeot', '206', 'Essence'),
(14, 'Peugeot', '206', 'Gazole'),
(15, 'Peugeot', '206', 'GPL'),
(16, 'Peugeot', '206', 'Electric'),
(17, 'Citroen', 'C4', 'Essence'),
(18, 'Citroen', 'C4', 'Gazole'),
(19, 'Citroen', 'C4', 'GPL'),
(20, 'Citroen', 'C4', 'Electric'),
(21, 'Citroen', 'C5', 'Essence'),
(22, 'Citroen', 'C5', 'Gazole'),
(23, 'Citroen', 'C5', 'GPL'),
(24, 'Citroen', 'C5', 'Electric'),
(25, 'Ford', 'Focus', 'Essence'),
(26, 'Ford', 'Focus', 'Gazole'),
(27, 'Ford', 'Focus', 'GPL'),
(28, 'Ford', 'Focus', 'Electric'),
(29, 'Ford', 'Fiesta', 'Essence'),
(30, 'Ford', 'Fiesta', 'Gazole'),
(31, 'Ford', 'Fiesta', 'GPL'),
(32, 'Ford', 'Fiesta', 'Electric');

Answer 1

If you need unique/distinct set of (Brand,Model,Version) add all three column name in GROUP BY clause like this:
SELECT brand, model, version FROM cars
WHERE version = (SELECT version FROM cars GROUP BY version ORDER BY RAND() LIMIT 1)
GROUP BY brand, model, version

Answer 2

Here is what I was offered, it is not optimized but it works.
If someone with a suggestion I'm interested.
CREATE TABLE IF NOT EXISTS temp AS
SELECT
tb1.id AS id1,
tb1.brand AS brand1,
tb1.model AS model1,
tb1.version AS version1,
tb2.id AS id2,
tb2.brand AS brand2,
tb2.model AS model2,
tb2.version AS version2,
tb3.id AS id3,
tb3.brand AS brand3,
tb3.model AS model3,
tb3.version AS version3,
tb4.id AS id4,
tb4.brand AS brand4,
tb4.model AS model4,
tb4.version AS version4
FROM `cars` AS tb1
INNER JOIN `cars` AS tb2
ON tb2.brand != tb1.brand
AND tb2.model != tb1.model
AND tb2.version != tb1.version
AND tb2.id > tb1.id
INNER JOIN `cars` AS tb3
ON tb3.brand != tb2.brand
AND tb3.model != tb2.model
AND tb3.version != tb2.version
AND tb3.id > tb2.id
AND tb3.brand != tb1.brand
AND tb3.model != tb1.model
AND tb3.version != tb1.version
AND tb3.id > tb1.id
INNER JOIN `cars` AS tb4
ON tb4.brand != tb3.brand
AND tb4.model != tb3.model
AND tb4.version != tb3.version
AND tb4.id > tb3.id
AND tb4.brand != tb2.brand
AND tb4.model != tb2.model
AND tb4.version != tb2.version
AND tb4.id > tb2.id
AND tb4.brand != tb1.brand
AND tb4.model != tb1.model
AND tb4.version != tb1.version
AND tb4.id > tb1.id
LIMIT 1
--------------
select * from sample
--------------
+-----+---------+--------+----------+-----+---------+--------+----------+-----+---------+--------+----------+-----+--------+--------+----------+
| id1 | brand1 | model1 | version1 | id2 | brand2 | model2 | version2 | id3 | brand3 | model3 | version3 | id4 | brand4 | model4 | version4 |
+-----+---------+--------+----------+-----+---------+--------+----------+-----+---------+--------+----------+-----+--------+--------+----------+
| 1 | Renault | Clio | Essence | 10 | Peugeot | 307 | Gazole | 19 | Citroen | C4 | GPL | 28 | Ford | Focus | Electric |
+-----+---------+--------+----------+-----+---------+--------+----------+-----+---------+--------+----------+-----+--------+--------+----------+
and get the result formatter
SELECT id1 AS id,
brand1 AS brand,
model1 AS model,
version1 AS version
FROM temp
UNION
SELECT id2 AS id,
brand2 AS brand,
model2 AS model,
version2 AS version
FROM temp
UNION
SELECT id3 AS id,
brand3 AS brand,
model3 AS model,
version3 AS version
FROM temp
UNION
SELECT id4 AS id,
brand4 AS brand,
model4 AS model,
version4 AS version
FROM temp
+----+---------+-------+----------+
| id | brand | model | version |
+----+---------+-------+----------+
| 1 | Renault | Clio | Essence |
| 10 | Peugeot | 307 | Gazole |
| 19 | Citroen | C4 | GPL |
| 28 | Ford | Focus | Electric |
+----+---------+-------+----------+