updated: 2022-01-23_12:32:31-05:00

Key

• See Foreign Key and Primary Key
• let K $\subseteq$ R
  • K is a Superkey of R if values for K are sufficient to identify a unique tuple of each possible relation r(R)
  • EG: {ID} and {ID,name} are superkeys of instructor
• Superkey K is a Candidate Key if K is minimal
• One of the Candidate Keys is chosen to be the Primary Key
• Foreign Key constraint: Value in one relation must appear in another:
  • Referencing relation
  • Referenced relation
  • EG: dept_name in instructor is a foreign key from instructor referencing department