SQL: Add New Admin User. In the example below, I am using an ID of 2. Change this number to the next user available, or some safe high number.

new-admin.sql

INSERT INTO databasename.wp_users (ID, user_login, user_pass, user_nicename, user_email, user_url, user_registered, user_activation_key, user_status, display_name) VALUES ('2', 'admin_demo', MD5('demo_password'), 'Travis Smith', 'no-reply@wpsmith.net', 'http://wpsmith.net/', '2014-02-15 00:00:00', '', '0', 'Travis Smith');
INSERT INTO databasename.wp_usermeta (umeta_id, user_id, meta_key, meta_value) VALUES (NULL, '2', 'wp_capabilities', 'a:1:{s:13:"administrator";s:1:"1";}');
INSERT INTO databasename.wp_usermeta (umeta_id, user_id, meta_key, meta_value) VALUES (NULL, '2', 'wp_user_level', '10');

INSERT INTO databasename.myprefix_users (ID, user_login, user_pass, user_nicename, user_email, user_url, user_registered, user_activation_key, user_status, display_name) VALUES ('2', 'admin_demo', MD5('demo_password'), 'Travis Smith', 'no-reply@wpsmith.net', 'http://wpsmith.net/', '2014-02-15 00:00:00', '', '0', 'Travis Smith');
INSERT INTO databasename.myprefix_usermeta (umeta_id, user_id, meta_key, meta_value) VALUES (NULL, '2', 'myprefix_capabilities', 'a:1:{s:13:"administrator";s:1:"1";}');
INSERT INTO databasename.myprefix_usermeta (umeta_id, user_id, meta_key, meta_value) VALUES (NULL, '2', 'myprefix_user_level', '10');

For more information, see the tutorial here: http://wpsmith.net/2014/snippets/popular-wordpress-sql-user-administration-scripts/