WHEN condition postgresql evaluate the result

Question

I dont't understand why the when condition evaluate the result if it is FALSE.

FOR EXAMPLE:

WHERE
    CASE
        WHEN false THEN lower(pmo.id_province) <> lower(dp.id_province)
        WHEN true THEN pmo.id_province <> dp.id_province 
    END;

Here postgresqll's message:

ERROR: function lower(integer) does not exist LINE 8: WHEN false THEN lower(pmo.id_province) <> lower(dp.id_prov... ^ HINT: No function matches the given name and argument types. You might need to add explicit type casts. SQL state: 42883 Character: 199

I know that lower function accept text arguments, but I inserted the when statements for avoid this issue, but not work. Why WHEN by pass the condition if it is false?

Answer 1

It is not executed, but it failing before execution, when it tries to resolve which functions are being referenced. That happens at parse time, not during execution.