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Table icons {
  icon_id integer [primary key]
  file_name varchar
}

Table categories {
  category_id integer [primary key]
  icon_id integer
  category_name varchar
}
Ref: categories.icon_id < icons.icon_id

Table priorities {
  priority_id integer [primary key]
  priority_name varchar
}

Table tasks {
  task_id integer [primary key]
  title varchar
  priority_id integer
  category_id integer
  description varchar
  expire_date_time timestamp
  deleted boolean
  completed boolean
}
Ref: tasks.priority_id < priorities.priority_id
Ref: tasks.category_id < categories.category_id