-- Add screen_name column to db_users_d table
ALTER TABLE `db_users_d` 
ADD COLUMN `screen_name` VARCHAR(75) NOT NULL DEFAULT '-' AFTER `id`;

-- Update existing records to copy screen_name from db_users_a
UPDATE `db_users_d` ud
INNER JOIN `db_users_a` ua ON ud.id = ua.id
SET ud.screen_name = ua.screen_name;




