How to Mass Delete Unapproved Comments from Your WordPress Database Using phpMyAdmin
IMPORTANT MESSAGE: If you use the Bigdump script I illustrate below, after you are done importing your database, be sure to delete the Bigdump directory. If you leave it in place, then anyone who stumbles across it could destroy your database. So, once you are done, remove it from your server and then if you need to use it again in the future, just upload it when you need it…removing it when you are done with it.
How to Import a Large WordPress Database — An Alternative to phpMyAdmin — Part 1 of 2