4.3.3 Joining things up

• Joining table


  A table that lists every relationship between every entity in a relational database
• Relationships are stored in a joining table
• Joining table


  • Each record represents a single relationship between entities
  • Student keys appearing more than once shows an individual student studies many courses
  • Course codes listed multiple times shows the course is being taken by many students
• Many-to-many relationship


  A relationship where an entity on one side is related to multiple entities on the other side, and vice versa
• Querying a relational database to find courses taken by a student


  1. Query Student_Table to get student's key

  2. Use student's key to query Student_Allocation_Table to get course codes

  3. Query Course_Table to get course titles
• The complexity of the database is hidden from the user
• Entities in the committee meeting database


  • Committee
  • Member
• Key field


  A field that uniquely identifies each record in a table
• A joining table is needed to represent the many-to-many relationship between committees and members