Use the below code snippets to clean up spam comments as shown in video above. Remember to FIRST do an EXPORT (Backup) of your Database BEFORE doing any of the querrys.
Mass Delete all Spam Comments
DELETE FROM wp_comments WHERE comment_approved = 'spam';
Mass Delete all Trash Comments
DELETE FROM wp_comments WHERE comment_approved = 'trash';
Mass Delete all Approved Comments
DELETE FROM wp_comments WHERE comment_approved = '1';
Mass Delete all Pending Comments
DELETE FROM wp_comments WHERE comment_approved = '0';
Important!
Make sure the prefix is correct for your db. If it is not the default wp or something you made custom, then replace wp with your custom prefix.
For example, I changed my prefix from wp into bgws so my query must be like this:
DELETE FROM bgws_comments WHERE comment_approved = '0';