Solution:Step 1: Understand ON UPDATE CASCADE effectON UPDATE CASCADE updates child foreign keys automatically when parent keys change.Step 2: Apply update to parent and childParent id changes from 1 to 2, so child.parent_id updates from 1 to 2 automatically.Final Answer:2 -> Option AQuick Check:ON

[Solved] Given 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 UPDATE CASCADE);INSERT INTO parent... | SQL

SQL - Table Constraints

Given 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 UPDATE CASCADE
);
INSERT INTO parent VALUES (1);
INSERT INTO child VALUES (10, 1);
UPDATE parent SET id = 2 WHERE id = 1;

What will be the value of parent_id in the child table after the update?

A2

BUpdate fails with error

CNULL

D1

Step-by-Step Solution

Solution:

Step 1: Understand ON UPDATE CASCADE effect
ON UPDATE CASCADE updates child foreign keys automatically when parent keys change.
Step 2: Apply update to parent and child
Parent id changes from 1 to 2, so child.parent_id updates from 1 to 2 automatically.
Final Answer:
2 -> Option A
Quick Check:
ON UPDATE CASCADE updates child keys = 2 [OK]

Quick Trick: CASCADE updates child keys to new parent key value [OK]

Common Mistakes:

MISTAKES

Expecting child key to stay the same
Thinking update causes error
Assuming child key becomes NULL

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More SQL Quizzes

Given these tables:

Step 1: Understand ON UPDATE CASCADE effect

Step 2: Apply update to parent and child

Final Answer:

Quick Check:

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