MySQL: ALTER IGNORE TABLE gives “Integrity constraint violation”

Question

I\'m trying to remove duplicates from a MySQL table using ALTER IGNORE TABLE + an UNIQUE KEY. The MySQL documentation says:

IGNORE is a MySQL extensio

Answer 1

The problem is that you have duplicate data in the field you're trying to index. You'll need to remove the offending duplicates before you can add a unique index.

One way is to do the following:

   CREATE TABLE tmp_table LIKE table;
   ALTER IGNORE TABLE tmp_table ADD UNIQUE INDEX dupidx (field);
   INSERT IGNORE INTO tmp_table SELECT * FROM table;
   DROP TABLE table;
   RENAME TABLE tmp_table TO table;

this allows you to insert only the unique data into the table