[Solved] A developer wrote this table creation:CREATE TABLE orders (order_id INT PRIMARY KEY, customer_id INT NOT NULL, FOREIGN KEY (customer_id) REFERENCES customers(id) ON DELETE SET NULL);But the database... | SQL

SQL - Database Design and Normalization

A developer wrote this table creation:

CREATE TABLE orders (order_id INT PRIMARY KEY, customer_id INT NOT NULL, FOREIGN KEY (customer_id) REFERENCES customers(id) ON DELETE SET NULL);

But the database throws an error. What is the likely cause?

AON DELETE SET NULL is not supported in SQL

BPrimary key cannot be on order_id

CFOREIGN KEY syntax is incorrect

Dcustomer_id column is not nullable but ON DELETE SET NULL requires it

Step-by-Step Solution

Solution:

Step 1: Understand ON DELETE SET NULL requirement
This action sets foreign key column to NULL on delete, so column must allow NULL.
Step 2: Check customer_id nullability
If customer_id is NOT NULL, the action causes error because NULL cannot be assigned.
Final Answer:
customer_id column is not nullable but ON DELETE SET NULL requires it -> Option D
Quick Check:
ON DELETE SET NULL requires nullable foreign key column [OK]

Quick Trick: Nullable foreign keys needed for ON DELETE SET NULL [OK]

Common Mistakes:

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