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MySQL: Remove duplicate entries
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Remove duplicate entries. Assume the following table and data.
CREATE TABLE IF NOT EXISTS dupTest (
pkey int(11) NOT NULL auto_increment,
a int,
b int,
c int,
timeEnter timestamp(14),
PRIMARY KEY (pkey)
);
insert into dupTest (a,b,c) values (1,2,3),(1,2,3),
(1,5,4),(1,6,4);
mysql> select * from dupTest;
select * from dupTest;
+------+------+------+------+---------------------+
| pkey | a | b | c | timeEnter |
+------+------+------+------+---------------------+
| 1 | 1 | 2 | 3 | 2004-04-16 10:55:35 |
| 2 | 1 | 2 | 3 | 2004-04-16 10:55:35 |
| 3 | 1 | 5 | 4 | 2004-04-16 10:55:35 |
| 4 | 1 | 6 | 4 | 2004-04-16 10:55:35 |
+------+------+------+------+---------------------+
4 rows in set (0.00 sec)
mysql>
Note, the first two rows contains duplicates in columns a and b. It contains
other duplicates; but, leaves the other duplicates alone.
mysql> ALTER IGNORE TABLE dupTest ADD UNIQUE INDEX(a,b);
mysql> select * from dupTest;
select * from dupTest;
+------+------+------+------+---------------------+
| pkey | a | b | c | timeEnter |
+------+------+------+------+---------------------+
| 1 | 1 | 2 | 3 | 2004-04-16 11:11:42 |
| 3 | 1 | 5 | 4 | 2004-04-16 11:11:42 |
| 4 | 1 | 6 | 4 | 2004-04-16 11:11:42 |
+------+------+------+------+---------------------+
3 rows in set (0.00 sec)
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About the author of this programming example or tutorial:
Mike Chirico (mchirico@users.sourceforge.net)
Copyright (c) 2004 (GPU Free Documentation License)
Last Updated: Tue Jul 20 12:14:51 EDT 2004
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