[Solved] A parent table has a foreign key referenced by a child table with ON DELETE CASCADE. You want to prevent deletion of a parent row if any child rows exist, but keep the cascade for some cases.... | SQL

SQL - Table Constraints

A parent table has a foreign key referenced by a child table with ON DELETE CASCADE. You want to prevent deletion of a parent row if any child rows exist, but keep the cascade for some cases. How can you achieve this?

AUse triggers to check child rows before delete and raise error if any exist.

BChange ON DELETE CASCADE to ON DELETE RESTRICT.

CRemove the foreign key constraint and handle deletes manually.

DSet foreign key to ON DELETE SET NULL.

Step-by-Step Solution

Solution:

Step 1: Understand ON DELETE CASCADE behavior
CASCADE always deletes child rows automatically.
Step 2: Prevent deletion conditionally
Using triggers allows custom logic to block deletes when child rows exist, while allowing cascade in other cases.
Final Answer:
Use triggers to check child rows before delete and raise error if any exist. -> Option A
Quick Check:
Triggers enable conditional delete control [OK]

Quick Trick: Use triggers for conditional delete control [OK]

Common Mistakes:

MISTAKES

Assuming ON DELETE CASCADE can be conditional
Removing constraints causes data integrity issues
Confusing RESTRICT with conditional cascade

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How can you achieve this?

Step 1: Understand ON DELETE CASCADE behavior

Step 2: Prevent deletion conditionally

Final Answer:

Quick Check:

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