MySQL 删除重复记录

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A really easy way to do this is to add a UNIQUE index on the 3 columns. When you write the ALTER statement, include the IGNORE keyword. Like so:

ALTER IGNORE TABLE jobs ADD UNIQUE INDEX idx_name (site_id, title, company );

This will drop all the duplicate rows. As an added benefit, future INSERTs that are duplicates will error out. As always, you may want to take a backup before running something like this...

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Another possible solution that I've just come across:

DELETE n1 FROM names n1, names n2 WHERE n1.id > n2.id AND n1.name = n2.name

if you want to keep the row with the lowest id value OR

DELETE n1 FROM names n1, names n2 WHERE n1.id < n2.id AND n1.name = n2.name

if you want to keep the row with the highest id value.

I used this method in MySQL 5.1

Not sure about other versions.

*NB - You need to do this first on a test copy of your table!+ When I did it, I found that unless I also included AND n1.id <> n2.id, it deleted every row in the table.

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Add Unique Index on your table:

ALTER IGNORE TABLE `TableA`   
ADD UNIQUE INDEX (`member_id`, `quiz_num`, `question_num`, `answer_num`);

OR

Add primry key in your table then you can easily remove duplicates from your table using below query:

DELETE FROM member  
WHERE id IN (SELECT *
             FROM (SELECT id FROM member
                   GROUP BY member_id, quiz_num, question_num, answer_num HAVING (COUNT(*) > 1)
                  ) AS A
            );

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REF:

http://stackoverflow.com/questions/3311903/remove-duplicate-rows-in-mysql

http://stackoverflow.com/questions/4685173/delete-all-duplicate-rows-except-for-one-in-mysql

http://stackoverflow.com/questions/14046355/how-do-i-delete-all-the-duplicate-records-in-a-mysql-table-without-temp-tables