-- =============================================
-- Education 模块 — 答案保存幂等性回滚
-- Ticket #7 / Migration 003
-- =============================================
--
-- WARNING: This file contains NO executable SQL.
-- Destructive rollback requires manual operator verification.
--
-- Manual rollback procedure (operator must execute):
-- 1. Verify no other tables depend on education_answer_idempotency:
--      SELECT TABLE_NAME, COLUMN_NAME, REFERENCED_TABLE_NAME
--        FROM information_schema.KEY_COLUMN_USAGE
--       WHERE REFERENCED_TABLE_NAME = 'education_answer_idempotency'
--         AND TABLE_SCHEMA = DATABASE();
--    Result MUST be empty before proceeding.
--
-- 2. Verify the table contains only data from this migration:
--      SELECT COUNT(*) AS idempotency_count FROM education_answer_idempotency;
--    Operator must confirm this count is acceptable to destroy.
--
-- 3. Verify no application code depends on client_sequence column:
--    Search codebase for 'clientSequence' / 'client_sequence' references.
--
-- 4. After verification, execute:
--      DROP TABLE IF EXISTS education_answer_idempotency;
--      ALTER TABLE education_practice_question DROP COLUMN client_sequence;
--
-- DO NOT uncomment or execute the lines below without operator verification.
-- -- DROP TABLE IF EXISTS education_answer_idempotency;
-- -- ALTER TABLE education_practice_question DROP COLUMN client_sequence;