update if exists [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

How do I update if exists, insert if not (aka upsert or merge) in MySQL?

I have a table with the columns user, category and score. I want to run a开发者_如何学JAVAn insert that, if this user/category combination already exists instead just updates the score. Both the user and the category column can have the same value many times but each specific user/category combination may only exist on one single row. How can I do this?

Many thanks

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For this example, let's call your table scores:

Make sure you have a unique index

ALTER TABLE scores ADD UNIQUE INDEX user_category_ndx (user,category);

Now run this to replace:

INSERT INTO scores (user,category,score) VALUES ('username','mycat',127)
ON DUPLICATE KEY UPDATE score = VALUES(score);

If your updating the score means add up scores, then do this:

INSERT INTO scores (user,category,score) VALUES ('username','mycat',127)
ON DUPLICATE KEY UPDATE score = score + VALUES(score);

Give it a try!

UPDATE 2011-08-28 09:00 EDT

If you want to keep just high scores and then add the unique index, here is what you must do:

CREATE TABLE scores_new LIKE scores;
ALTER TABLE scores_new ADD UNIQUE INDEX user_category_ndx (user,category);
INSERT INTO scores_new (user,category,score)
SELECT user,category,MAX(score) FROM scores GROUP BY user,category;
ALTER TABLE scores RENAME scores_old;
ALTER TABLE scores_new RENAME scores;
#
# Drop old table if no longer needed
#
DROP TABLE scores_old;

UPDATE 2011-08-28 10:53 EDT

Run this to keep maximum score:

INSERT INTO scores (user,category,score) VALUES ('username','mycat',127)
ON DUPLICATE KEY UPDATE score = GREATEST(VALUES(score),score);

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What you want is INSERT ... ON DUPLICATE KEY UPDATE. Make sure you have a unique index defined on user, category. See http://dev.mysql.com/doc/refman/5.1/en/insert-on-duplicate.html