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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