Keys

• Primary key

  • Every table (object) must have a primary key
  • Uniquely identifies a row (one-to-one)

• Concatenated (or composite) key

  • Multiple columns needed for primary key
  • Identify repeating relationships (1 : M or M : N)

• Key columns are underlined

• First step

  • Collect user documents
  • Identify possible keys: unique or repeating relationships

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