-- Platform question bank extension. Execute after 2026-09-15-exam.sql.
-- Existing teacher questions remain usable and are classified as TEACHER.
ALTER TABLE exam_question
  ADD COLUMN source_type varchar(16) NOT NULL DEFAULT 'TEACHER' COMMENT '题目来源：PLATFORM/TEACHER',
  ADD COLUMN task_key varchar(128) NULL COMMENT '归属实训任务，关联 training_task.task_key';

UPDATE exam_question SET source_type='TEACHER' WHERE source_type IS NULL OR source_type='';

ALTER TABLE exam_question
  ADD KEY idx_exam_question_source_task (source_type, task_key),
  ADD KEY idx_exam_question_task (task_key);