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Why do weak entities require composite primary keys including the owner entity's key in relational tables?

hard📝 Conceptual Q10 of 15
SQL - Table Relationships
Why do weak entities require composite primary keys including the owner entity's key in relational tables?
ABecause weak entities lack sufficient attributes to form a unique key alone
BBecause weak entities always have more attributes than owner entities
CBecause weak entities cannot be represented as tables
DBecause owner entity keys are always strings
Step-by-Step Solution
Solution:

  1. Step 1: Understand weak entity uniqueness

    Weak entities do not have enough attributes to uniquely identify records alone.

  2. Step 2: Explain composite key necessity

    Including owner entity's key ensures uniqueness by combining keys.

  3. Final Answer:

    Because weak entities lack sufficient attributes to form a unique key alone -> Option A

  4. Quick Check:

    Weak entity uniqueness needs composite key [OK]
Quick Trick: Weak entities need owner keys for uniqueness [OK]
Common Mistakes:
MISTAKES
  • Assuming weak entities have unique keys alone
  • Confusing attribute count with key necessity
  • Thinking weak entities can't be tables

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