[Solved] You have a table orders with columns order_id (primary key), customer_id, and order_date.... Which of these statements has an error? | SQL

SQL - Database Design and Normalization

You have a table orders with columns order_id (primary key), customer_id, and order_date. You want to add a foreign key constraint on customer_id referencing customers(customer_id). Which of these statements has an error?

AALTER TABLE orders ADD FOREIGN KEY (customer_id) REFERENCES customers(customer_id);

BALTER TABLE orders ADD CONSTRAINT fk_customer FOREIGN KEY (customer_id) REFERENCES customers(customer_id);

CALTER TABLE orders ADD FOREIGN KEY customer_id REFERENCES customers(customer_id);

DALTER TABLE orders ADD CONSTRAINT fk_customer FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE CASCADE;

Step-by-Step Solution

Solution:

Step 1: Review correct syntax for adding foreign keys
The correct syntax requires parentheses around the column name after FOREIGN KEY.
Step 2: Identify the incorrect statement
ALTER TABLE orders ADD FOREIGN KEY customer_id REFERENCES customers(customer_id); misses parentheses around customer_id, causing syntax error.
Final Answer:
ALTER TABLE orders ADD FOREIGN KEY customer_id REFERENCES customers(customer_id); -> Option C
Quick Check:
Foreign key column must be in parentheses [OK]

Quick Trick: Always use parentheses around foreign key columns [OK]

Common Mistakes:

Omitting parentheses around column names
Forgetting to name the constraint (optional but recommended)
Misplacing ON DELETE options

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Which of these statements has an error?

Step 1: Review correct syntax for adding foreign keys

Step 2: Identify the incorrect statement

Final Answer:

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