How to keep only one row of a table, removing duplicate rows?

See the following question: Deleting duplicate rows from a table.

The adapted accepted answer from there (which is my answer, so no "theft" here...):

You can do it in a simple way assuming you have a unique ID field: you can delete all records that are the same except for the ID, but don't have "the minimum ID" for their name.

Example query:

DELETE FROM members
WHERE ID NOT IN
(
    SELECT MIN(ID)
    FROM members
    GROUP BY name
)

In case you don't have a unique index, my recommendation is to simply add an auto-incremental unique index. Mainly because it's good design, but also because it will allow you to run the query above.

It would probably be easier to select the unique ones into a new table, drop the old table, then rename the temp table to replace it.

#create a table with same schema as members
CREATE TABLE tmp (...);

#insert the unique records
INSERT INTO tmp SELECT * FROM members GROUP BY name;

#swap it in
RENAME TABLE members TO members_old, tmp TO members;

#drop the old one
DROP TABLE members_old;