-- 清理 t_employee 中重复邮箱（仅保留同邮箱组内 employee_id 最小的一条）
-- 背景：唯一性校验 getByEmail 使用 selectOne，若同邮箱存在多条未删除记录会触发 TooManyResultsException

UPDATE t_employee e
SET email       = NULL,
    update_time = NOW()
WHERE e.deleted_flag = false
  AND e.email IS NOT NULL
  AND trim(e.email) <> ''
  AND EXISTS (
      SELECT 1
      FROM t_employee o
      WHERE o.deleted_flag = false
        AND o.email = e.email
        AND o.employee_id < e.employee_id
  );