docs: Add initial ERD for e-learning platform database schema.

ERD v.1.txt

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+Table users {
+  id int [pk
+  ]
+  name varchar
+  email varchar [unique
+  ]
+  password varchar
+  role varchar // admin | instructor | learner
+  created_at datetime
+  updated_at datetime
+}
+
+Table courses {
+  id int [pk
+  ]
+  categories_id int
+  title jsonb // { "th": "...", "en": "..." }
+  description jsonb // { "th": "...", "en": "..." }
+  price decimal
+  is_free boolean
+  status varchar // draft | pending | approved | rejected
+  instructor_id int
+  approved_by int // admin user id
+  created_at datetime
+  updated_at datetime
+}
+
+Table categories {
+  id int [pk
+  ]
+  name jsonb // multi-language category name
+  description jsonb // optional
+  created_at datetime
+  updated_at datetime
+}
+
+Table chapters {
+  id int [pk
+  ]
+  course_id int
+  title jsonb // multi-language
+  sort_order int
+  created_at datetime
+  updated_at datetime
+}
+
+Table lessons {
+  id int [pk
+  ]
+  chapter_id int
+  title jsonb // multi-language
+  content jsonb // multi-language lesson content
+  type varchar // video | pdf | text | quiz
+  sort_order int
+  created_at datetime
+  updated_at datetime
+}
+
+Table quizzes {
+  id int [pk
+  ]
+  lesson_id int
+  title jsonb // multi-language
+  passing_score int
+  time_limit int
+  created_at datetime
+  updated_at datetime
+}
+
+Table questions {
+  id int [pk
+  ]
+  quiz_id int
+  question jsonb // multi-language
+  score int
+  created_at datetime
+  updated_at datetime
+}
+
+Table choices {
+  id int [pk
+  ]
+  question_id int
+  text jsonb // multi-language
+  is_correct boolean
+  created_at datetime
+  updated_at datetime
+}
+
+Table enrollments {
+  id int [pk
+  ]
+  user_id int
+  course_id int
+  status varchar // enrolled | completed
+  enrolled_at datetime
+  created_at datetime
+  updated_at datetime
+}
+
+Table announcements {
+  id int [pk
+  ]
+  course_id int
+  instructor_id int
+  title jsonb // multi-language
+  content jsonb // multi-language
+  is_pinned boolean // pin important announcements to top
+  published_at datetime // scheduled publish date
+  created_at datetime
+  updated_at datetime
+}
+
+Table announcement_attachments {
+  id int [pk
+  ]
+  announcement_id int
+  file_name varchar
+  file_path varchar
+  file_size int
+  mime_type varchar
+  created_at datetime
+}
+
+Table orders {
+  id int [pk
+  ]
+  user_id int
+  total_amount decimal
+  status varchar // pending | paid | cancelled
+  created_at datetime
+  updated_at datetime
+}
+
+Table order_items {
+  id int [pk
+  ]
+  order_id int
+  course_id int
+  price decimal
+  created_at datetime
+  updated_at datetime
+}
+
+Table payments {
+  id int [pk
+  ]
+  order_id int
+  provider varchar
+  transaction_id varchar
+  amount decimal
+  status varchar // success | failed
+  paid_at datetime
+  created_at datetime
+  updated_at datetime
+}
+
+Table instructor_balances {
+  id int [pk
+  ]
+  instructor_id int
+  available_amount decimal
+  withdrawn_amount decimal
+  created_at datetime
+  updated_at datetime
+}
+
+Table withdrawal_requests {
+  id int [pk
+  ]
+  instructor_id int
+  amount decimal
+  status varchar // pending | approved | rejected | paid
+  approved_by int
+  created_at datetime
+  updated_at datetime
+}
+
+Ref: courses.instructor_id > users.id
+Ref: courses.approved_by > users.id
+
+Ref: courses.categories_id > categories.id
+
+Ref: chapters.course_id > courses.id
+Ref: lessons.chapter_id > chapters.id
+Ref: quizzes.lesson_id > lessons.id
+Ref: questions.quiz_id > quizzes.id
+Ref: choices.question_id > questions.id
+
+Ref: enrollments.user_id > users.id
+Ref: enrollments.course_id > courses.id
+
+Ref: announcements.course_id > courses.id
+Ref: announcements.instructor_id > users.id
+Ref: announcement_attachments.announcement_id > announcements.id
+
+Ref: orders.user_id > users.id
+Ref: order_items.order_id > orders.id
+Ref: order_items.course_id > courses.id
+Ref: payments.order_id > orders.id
+
+Ref: instructor_balances.instructor_id > users.id
+Ref: withdrawal_requests.instructor_id > users.id
+Ref: withdrawal_requests.approved_by > users.id