How To Delete All Comments In wordpress

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Any one explain How To Delete All Comments In wordpress

Install Plugin 1 or 2 ::

1. Delete Pending Comments Version 0.2.1.1
Dashboard -> Comment -> Delete Pending Comments

Or

2. WP-Optimize Version 0.9.4
Dashboard -> WP-Optimize -> Comment ->

Clean marked Spam comments
Clean Unapproved comments

3. Dashboard -> Settings-> Discussion -> (Check the settings, can disable comment)

4. WP-Optimize had other functions also.