Postgresql, Restrict update on specific columns (Read Only)

postgresql

Solution

The easiest way is to create `BEFORE UPDATE` trigger that will compare `OLD` and `NEW` row and `RAISE EXCEPTION` if the change to the row is forbidden.

Problem

Is it possible to have postresql restrict/prevent an update on a specific record if the update includes changes to specific columns? How would this be implemented. A trigger/constraint? What would be the most efficient way to implement this? I am using version 9.1

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