erDiagram
grades {
integer id
string grade_name
datetime created_at
datetime updated_at
}
students {
integer id
string card_number
string student_name
integer grade_id
datetime created_at
datetime updated_at
}
missions {
integer id
string mission_name
integer reward_stamp_count
datetime created_at
datetime updated_at
}
stamp_operations {
integer id
integer student_id
integer mission_id
integer actual_reward_stamp_count
datetime created_at
datetime updated_at
}
students ||--o{ stamp_operations : N-N
missions ||--o{ stamp_operations : N-N
grades ||--o{ students : students