[Solved] Consider these tables:CREATE TABLE parent (id INT PRIMARY KEY);CREATE TABLE child (id INT PRIMARY KEY, parent_id INT, FOREIGN KEY (parent_id) REFERENCES parent(id) ON DELETE SET NULL);INSERT INTO... | SQL

SQL - Table Constraints

Consider these tables:

CREATE TABLE parent (id INT PRIMARY KEY);
CREATE TABLE child (id INT PRIMARY KEY, parent_id INT, FOREIGN KEY (parent_id) REFERENCES parent(id) ON DELETE SET NULL);
INSERT INTO parent VALUES (1);
INSERT INTO child VALUES (10, 1);
DELETE FROM parent WHERE id = 1;

What is the value of parent_id in the child row after the delete?

A1

BNULL

C0

DThe row is deleted

Step-by-Step Solution

Solution:

Step 1: Recall ON DELETE SET NULL behavior
When parent row is deleted, child foreign key is set to NULL.
Step 2: Apply to the child row
Child row's parent_id changes from 1 to NULL after parent deletion.
Final Answer:
parent_id is set to NULL in the child row. -> Option B
Quick Check:
ON DELETE SET NULL sets foreign key to NULL [OK]

Quick Trick: SET NULL clears foreign key on parent delete [OK]

Common Mistakes:

MISTAKES

Assuming child row is deleted
Thinking foreign key remains unchanged
Confusing NULL with zero

Master "Table Constraints" in SQL

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More SQL Quizzes

Consider these tables:

Step 1: Recall ON DELETE SET NULL behavior

Step 2: Apply to the child row

Final Answer:

Quick Check:

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