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MySQL 5.5 Reference Manual
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MySQL 5.5 Reference Manual  /  ...  /  PRIMARY KEY and UNIQUE Index Constraints PRIMARY KEY and UNIQUE Index Constraints

Normally, errors occur for data-change statements (such as INSERT or UPDATE) that would violate primary-key, unique-key, or foreign-key constraints. If you are using a transactional storage engine such as InnoDB, MySQL automatically rolls back the statement. If you are using a nontransactional storage engine, MySQL stops processing the statement at the row for which the error occurred and leaves any remaining rows unprocessed.

MySQL supports an IGNORE keyword for INSERT, UPDATE, and so forth. If you use it, MySQL ignores primary-key or unique-key violations and continues processing with the next row. See the section for the statement that you are using (Section 13.2.5, “INSERT Syntax”, Section 13.2.11, “UPDATE Syntax”, and so forth).

You can get information about the number of rows actually inserted or updated with the mysql_info() C API function. You can also use the SHOW WARNINGS statement. See Section, “mysql_info()”, and Section, “SHOW WARNINGS Syntax”.

Only InnoDB tables support foreign keys. See Section, “InnoDB and FOREIGN KEY Constraints”.

User Comments
  Posted by hamy t on January 4, 2009
Quick Example of ignoring a unique key

Here is our table:
CREATE TABLE `file_names` (
`id` int(11) NOT NULL auto_increment,
`file_name` text NOT NULL,
UNIQUE KEY `file_name` (`file_name`(200))

Here is our query
INSERT IGNORE INTO `its_streamingdata`.`file_names` (`id` ,
`file_name`) VALUES (NULL , 'a'), (NULL , 'a')

The table now contains one row with a filename of 'a'

  Posted by DBA Lead on February 21, 2012
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