In a trigger function, you want to prevent updates that decrease the balance column. Which code snippet correctly enforces this?

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PostgreSQL - Triggers in PostgreSQL

In a trigger function, you want to prevent updates that decrease the balance column. Which code snippet correctly enforces this?

AIF NEW.balance > OLD.balance THEN RAISE EXCEPTION 'Balance cannot decrease'; END IF;

BIF NEW.balance = OLD.balance THEN RAISE EXCEPTION 'Balance cannot decrease'; END IF;

CIF OLD.balance < NEW.balance THEN RAISE EXCEPTION 'Balance cannot decrease'; END IF;

DIF NEW.balance < OLD.balance THEN RAISE EXCEPTION 'Balance cannot decrease'; END IF;

Step-by-Step Solution

Solution:

Step 1: Identify condition to block
We want to block if new balance is less than old balance (decrease).
Step 2: Write correct IF condition
IF NEW.balance < OLD.balance THEN raises exception to prevent decrease.
Final Answer:
IF NEW.balance < OLD.balance THEN RAISE EXCEPTION 'Balance cannot decrease'; END IF; -> Option D
Quick Check:
Block if NEW less than OLD [OK]

Quick Trick: Raise exception if NEW value is less than OLD to block decrease [OK]

Common Mistakes:

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