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Removing 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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MySQL 
