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SET AUTOCOMMIT = 0
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START TRANSACTION
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DROP DATABASE IF EXISTS `base`
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CREATE DATABASE `base`
DEFAULT CHARACTER SET `latin1`
DEFAULT COLLATE `latin1_general_ci`
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DROP TABLE IF EXISTS `test`
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CREATE TABLE `test`
( `id` INTEGER UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
`clef` VARCHAR(255) NOT NULL,
`col1` VARCHAR(255) NULL,
`col2` VARCHAR(255) NULL,
`col3` VARCHAR(255) NULL
) ENGINE=InnoDB
DEFAULT CHARSET=`latin1` COLLATE=`latin1_general_ci`
ROW_FORMAT=COMPRESSED
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insert into `test` (`clef`,`col1`,`col2`,`col3`) values
('alpha', null, null, 'rouge'),
('beta', null, 'vert', null),
('gamma', null, 'bleu', null),
('alpha', 'orange', null, null),
('beta', 'gris', null, null),
('gamma', null, null, 'violet'),
('alpha', null, 'jaune', null),
('beta', null, null, 'magenta'),
('gamma', 'turquoise', null, null)
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select * from `test`
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+----+-------+-----------+-------+---------+
| id | clef | col1 | col2 | col3 |
+----+-------+-----------+-------+---------+
| 1 | alpha | NULL | NULL | rouge |
| 2 | beta | NULL | vert | NULL |
| 3 | gamma | NULL | bleu | NULL |
| 4 | alpha | orange | NULL | NULL |
| 5 | beta | gris | NULL | NULL |
| 6 | gamma | NULL | NULL | violet |
| 7 | alpha | NULL | jaune | NULL |
| 8 | beta | NULL | NULL | magenta |
| 9 | gamma | turquoise | NULL | NULL |
+----+-------+-----------+-------+---------+
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create temporary table `temp` as
select clef,
max(col1) as col1,
max(col2) as col2,
max(col3) as col3
from test
group by clef
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select * from `temp`
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+-------+-----------+-------+---------+
| clef | col1 | col2 | col3 |
+-------+-----------+-------+---------+
| alpha | orange | jaune | rouge |
| beta | gris | vert | magenta |
| gamma | turquoise | bleu | violet |
+-------+-----------+-------+---------+
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delete t1 from test as t1
inner join test as t2
on t1.clef = t2.clef
and t1.id > t2.id
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select * from `test`
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+----+-------+------+------+-------+
| id | clef | col1 | col2 | col3 |
+----+-------+------+------+-------+
| 1 | alpha | NULL | NULL | rouge |
| 2 | beta | NULL | vert | NULL |
| 3 | gamma | NULL | bleu | NULL |
+----+-------+------+------+-------+
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update `test` as t1
inner join `temp` as t2
on t1.clef = t2.clef
set t1.col1 = t2.col1,
t1.col2 = t2.col2,
t1.col3 = t2.col3
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select * from `test`
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+----+-------+-----------+-------+---------+
| id | clef | col1 | col2 | col3 |
+----+-------+-----------+-------+---------+
| 1 | alpha | orange | jaune | rouge |
| 2 | beta | gris | vert | magenta |
| 3 | gamma | turquoise | bleu | violet |
+----+-------+-----------+-------+---------+
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COMMIT
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SET AUTOCOMMIT = 1
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