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| --------------
SET AUTOCOMMIT = 0
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--------------
START TRANSACTION
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--------------
DROP DATABASE IF EXISTS `base`
--------------
--------------
CREATE DATABASE `base`
DEFAULT CHARACTER SET `latin1`
DEFAULT COLLATE `latin1_general_ci`
--------------
--------------
DROP TABLE IF EXISTS `test`
--------------
--------------
CREATE TABLE `test`
(
`id` integer unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY,
`name` char(20) NOT NULL,
`visiteur` integer unsigned NOT NULL,
index `idx` (`name`,`visiteur`,`id`)
) ENGINE=InnoDB
DEFAULT CHARSET=`latin1` COLLATE=`latin1_general_ci`
ROW_FORMAT=COMPRESSED
--------------
--------------
INSERT INTO `test` (`name`, `visiteur`) VALUES
('un', 25),
('un', 163),
('un', 458),
('un', 13),
('deux', 13),
('trois', 33),
('trois', 75)
--------------
--------------
select * from test
--------------
+----+-------+----------+
| id | name | visiteur |
+----+-------+----------+
| 5 | deux | 13 |
| 6 | trois | 33 |
| 7 | trois | 75 |
| 4 | un | 13 |
| 1 | un | 25 |
| 2 | un | 163 |
| 3 | un | 458 |
+----+-------+----------+
--------------
select *
from test as tb1
where visiteur = (
select max(visiteur)
from test as tb2
where tb2.name = tb1.name
)
order by visiteur desc
--------------
+----+-------+----------+
| id | name | visiteur |
+----+-------+----------+
| 3 | un | 458 |
| 7 | trois | 75 |
| 5 | deux | 13 |
+----+-------+----------+
--------------
select c1.id, c1.name, c1.visiteur
from test c1
left outer join test c2
on c2.name = c1.name
and c2.visiteur > c1.visiteur
where c2.id is null
order by c1.visiteur desc
--------------
+----+-------+----------+
| id | name | visiteur |
+----+-------+----------+
| 3 | un | 458 |
| 7 | trois | 75 |
| 5 | deux | 13 |
+----+-------+----------+
--------------
explain
select *
from test as tb1
where visiteur = (
select max(visiteur)
from test as tb2
where tb2.name = tb1.name
)
order by visiteur desc
--------------
+----+--------------------+-------+-------+---------------+------+---------+---------------+------+------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+-------+-------+---------------+------+---------+---------------+------+------------------------------------------+
| 1 | PRIMARY | tb1 | index | NULL | idx | 28 | NULL | 8 | Using where; Using index; Using filesort |
| 2 | DEPENDENT SUBQUERY | tb2 | ref | idx | idx | 20 | base.tb1.name | 4 | Using index |
+----+--------------------+-------+-------+---------------+------+---------+---------------+------+------------------------------------------+
--------------
explain
select c1.id, c1.name, c1.visiteur
from test c1
left outer join test c2
on c2.name = c1.name
and c2.visiteur > c1.visiteur
where c2.id is null
order by c1.visiteur desc
--------------
+----+-------------+-------+-------+---------------+------+---------+--------------+------+--------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+------+---------+--------------+------+--------------------------------------+
| 1 | SIMPLE | c1 | index | NULL | idx | 28 | NULL | 8 | Using index; Using filesort |
| 1 | SIMPLE | c2 | ref | idx | idx | 20 | base.c1.name | 4 | Using where; Not exists; Using index |
+----+-------------+-------+-------+---------------+------+---------+--------------+------+--------------------------------------+
--------------
COMMIT
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SET AUTOCOMMIT = 1
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