Q:

How do I change the user via SQL?

I change a user via SQL in wordpress:
SET @old_user='old_user';
SET @new_user='new_user';

UPDATE wp_users SET user_login = replace(user_login, @old_user, @new_user);
UPDATE wp_users SET user_nicename = replace(user_nicename, @old_user, @new_user);
UPDATE wp_usermeta SET meta_value = replace(meta_value, @old_user, @new_user);

However, while posting a new one, the author is still the old one, for instace, 

Posted on October 3, 2015 by old_user. 

I must ignore something, please guide me.

A:

You probably haven't changed the display name, which is probably what is being displayed. "nicename" is used for the author's posts page url and not for display.
UPDATE wp_users SET display_name = replace(display_name, @old_user, @new_user);

