Probably there will be some applications that needs NULL result in situations when value was not changed or when input value has not expected format. Design using in Postgres allows later customization - you can implement with COALESCE very simply behave that you want (sure, you have to know what you do). If Postgres implement design used by MySQL, then there is not any possibility to react on situation when update is not processed.
A CASE _expression_ seems like it would work well for such detection in the rare case it is needed. Current behavior is unsafe with minimal or no redeeming qualities. Change it so passing in null raises an exception and make the user decide their own behavior if we don’t want to choose one for them.
David J.
