Avoiding inserting duplicate rows in mySQL

Question

I have a table with an auto_inc id (primary key). I am trying to avoid the insertion of duplicate rows.

Example of a duplicate row:

id  | field a | field b | field c |
1       4          6         7
2       4          6         7

The key (id) is not duplicate since it is automatically generated by MySQL, but all other fields are identical.

Answer 1

Make a unique index on fields a,b,c.

ALTER TABLE `table` ADD UNIQUE (
`a` ,
`b` ,
`c`
);

Answer 2

You should use ON DUPLICATE KEY UPDATE and declaring the fields as unique .

If you specify ON DUPLICATE KEY UPDATE, and a row is inserted that would cause a duplicate value in a UNIQUE index or PRIMARY KEY, an UPDATE of the old row is performed.

Answer 3

You can use this also.

INSERT INTO `tableName` ( `field1`, `field2`,`field3`)
SELECT `field1`, `field2`,`field3` FROM `tableName`
WHERE NOT EXISTS (SELECT 1
    FROM `tableName`
    WHERE 
    `field1` = 'value' AND `field2` = 'value'  AND `field3` = 'value'
    );

Answer 4

Make the three columns composite key.