mysql table createing new row instead of updating

Question

Instead of finding that a row exists where 'bookName' equals 'bookName' and just updating, it creates a brand new row. What is wrong with my command? thanks!

$query = mysql_query(
"INSERT INTO custombookinfo (userId, sendToAddress, work, caseStudies, url, entryPoint, date, bookName) 
 VALUES ('$userId', '$emailAddress', '$work', '$caseStudies', '$url', '$entryPoint', '$date', '$bookName') 
 ON DUPLICATE KEY UPDATE bookName = 'bookName'"
);

Answer 1

the INSERT query is correct but I think you have failed to define UNIQUE constraint on column bookName . Execute the following statement:

ALTER TABLE custombookinfo ADD CONSTRAINT tb_uq UNIQUE (bookName);

Answer 2

Depending on what you want to be UNIQUE in the table, you should create an index (PRIMARY or UNIQUE) for whether user_id, or bookName.

More details about INSERT ... ON DUPLICATE KEY UPDATE http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html