php - Bulk convert and update datetime column values to UNIX timestamp? -

background

i have mysql db around 16 million records. there 2 columns created_at , updated_at presently in datetime format.

the problem

i'd change unix timestamp converting values , updating records new values.

i know how php in loops, there way perform update executing single query in mysql?

as it'll 1 time change; can proceed way:

1. create new columns int datatypes , name them, say, created , updated.

   alter table `nameoftable`     add column `created` int unsigned not null default '0' after `created_at`,     add column `updated` int unsigned not null default '0' after `updated_at`; 

2. update table:

   update `nameoftable` set `created` = unix_timestamp( `created_at` ),     `updated` = unix_timestamp( `updated_at` ); 

3. remove older columns , rename newer ones created_at , updated_at.

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alternative way:

1. set datetime columns varchar field.

2. update using query:

   update `nameoftable` set `created_at` = unix_timestamp( `created_at` ),     `updated_at` = unix_timestamp( `updated_at` ); 

3. change columns int.