"Joel Jacobson" <joel(at)compiler(dot)org> writes:
> Is it idiomatic and safe to use
> SELECT
> CASE boolean_expression WHEN TRUE THEN function_with_side_effects() END
> in a query to ensure the function_with_side_effects() is only
> execute if boolean_expression is true?
As long as function_with_side_effects() is properly marked volatile,
it's safe (whether it's idiomatic is in the eye of the beholder).
The issue with the divide-by-zero example is that the division operator
is marked immutable, so if the planner sees that it has constant arguments
it will try to simplify-on-sight, even within a CASE expression.
regards, tom lane