Question

I have a table that has some duplicate results. For example:

`person_url`    `movie_url`
1                2
1                2
2                3

Would become –>

`person_url`    `movie_url`
1                2
2                3

I know how to do it by creating a new table,

create table tmp_credits (select distinct * from name);

However, it is a pretty large table and I have a couple indexes on it which will need to be re-created. How would I do this transformation in place, that is, without creating a new table?

Answer 1

You can add a UNIQUE index over your table’s columns using the IGNORE keyword:

ALTER IGNORE TABLE name ADD UNIQUE INDEX (person_url, movie_url);

As stated in the manual:

IGNORE is a MySQL extension to standard SQL. It controls how ALTER TABLE works if there are duplicates on unique keys in the new table or if warnings occur when strict mode is enabled. If IGNORE is not specified, the copy is aborted and rolled back if duplicate-key errors occur. If IGNORE is specified, only the first row is used of rows with duplicates on a unique key. The other conflicting rows are deleted. Incorrect values are truncated to the closest matching acceptable value.

This will also prevent duplicates from being added in the future.