oracle - Before update trigger is not creating history for null values -


my before update trigger not creating history changing null value other value. creating history changing other values. main logic this:

if nvl(:old.place,null) <> nvl(:new.place,null)     insert table (place)     values(:old.place) end if;

the nvl() function used substitute value in place of null. you're replacing null with... null, pointless. you're trying compare 2 null values (in)equality operator, , null neither equal or not equal including itself, result unknown, , condition false if either old or new value null.

you use fixed dummy value know never exit:

if nvl(:old.place,'**fake**') <> nvl(:new.place,'**fake**')

but clarity i'd prefer explicitly test nulls:

if (:old.place null , :new.place not null)   or (:old.place not null , :new.place null)   or (:old.place != :new.place)

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