[Solved] Why must a PostgreSQL trigger function always return either NEW or OLD row? — Ans: Because the trigger mechanism expects a row to continue or cancel the operation | PostgreSQL

PostgreSQL - Triggers in PostgreSQL

Why must a PostgreSQL trigger function always return either NEW or OLD row?

ABecause the trigger mechanism expects a row to continue or cancel the operation

BBecause returning void causes the trigger to run twice

CBecause returning NULL automatically commits the transaction

DBecause returning NEW or OLD triggers a database restart

Step-by-Step Solution

Solution:

Step 1: Understand trigger function return role
Trigger functions return NEW or OLD to tell PostgreSQL what row to use after the trigger runs.
Step 2: Explain consequences
Returning NEW continues with the modified row; returning OLD can cancel changes. Returning NULL skips the operation.
Final Answer:
Because the trigger mechanism expects a row to continue or cancel the operation -> Option A
Quick Check:
Trigger return value controls row operation continuation [OK]

Quick Trick: Return NEW or OLD to control row operation in triggers [OK]

Common Mistakes:

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Why must a PostgreSQL trigger function always return either NEW or OLD row?