If an ER diagram shows an entity Order(order_id, date) and a weak entity OrderItem(item_no, quantity) dependent on Order, which table design correctly represents this?

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SQL - Table Relationships

If an ER diagram shows an entity Order(order_id, date) and a weak entity OrderItem(item_no, quantity) dependent on Order, which table design correctly represents this?

AOrder(order_id, date, item_no), OrderItem(item_no, quantity)

BOrder(order_id, date), OrderItem(order_id, quantity)

COrder(order_id, date), OrderItem(item_no, quantity)

DOrder(order_id, date), OrderItem(order_id, item_no, quantity)

Step-by-Step Solution

Solution:

Step 1: Recognize weak entity key composition
OrderItem is weak and depends on Order, so its primary key includes order_id and item_no.
Step 2: Verify table design includes composite key
Order(order_id, date), OrderItem(order_id, item_no, quantity) includes order_id and item_no in OrderItem table, correctly modeling the weak entity.
Final Answer:
Order(order_id, date), OrderItem(order_id, item_no, quantity) -> Option D
Quick Check:
Weak entity table has composite key = Order(order_id, date), OrderItem(order_id, item_no, quantity) [OK]

Quick Trick: Weak entity keys combine owner key + own key [OK]

Common Mistakes:

MISTAKES

Missing owner key in weak entity table
Using only weak entity's own key
Placing weak entity attributes in owner table

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More SQL Quizzes

If an ER diagram shows an entity Order(order_id, date) and a weak entity OrderItem(item_no, quantity) dependent on Order, which table design correctly represents this?

Step 1: Recognize weak entity key composition

Step 2: Verify table design includes composite key

Final Answer:

Quick Check:

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