-- Drop the old foreign key constraint that links tasks to candidates.
-- The name 'tasks_ibfk_1' is the default name generated by MySQL.
ALTER TABLE `tasks` DROP FOREIGN KEY `tasks_ibfk_1`;

-- Drop the old column linking to candidates.
ALTER TABLE `tasks` DROP COLUMN `candidate_id`;

-- Add the new column to link tasks to employees (users).
ALTER TABLE `tasks` ADD COLUMN `assignee_id` INT;

-- Add the new foreign key constraint.
ALTER TABLE `tasks` ADD FOREIGN KEY (`assignee_id`) REFERENCES `users`(`id`) ON DELETE SET NULL;