https://www.postgresql.org/docs/current/plpgsql-trigger.html
>
> Row-level triggers fired BEFORE can return null to signal the trigger
> manager to skip the rest of the operation for this row (i.e., subsequent
> triggers are not fired, and the INSERT/UPDATE/DELETE does not occur for
> this row). If a nonnull value is returned then the operation proceeds with
> that row value. *Returning a row value different from the original value
> of NEW alters the row that will be inserted or updated. *Thus, if the
> trigger function wants the triggering action to succeed normally without
> altering the row value, NEW (or a value equal thereto) has to be
> returned. To alter the row to be stored, it is possible to replace single
> values directly in NEW and return the modified NEW, or to build a
> complete new record/row to return. In the case of a before-trigger on
> DELETE, the returned value has no direct effect, but it has to be nonnull
> to allow the trigger action to proceed. Note that NEW is null in DELETE
> triggers, so returning that is usually not sensible. The usual idiom in
> DELETE triggers is to return OLD.
>
I just want confirm the highlighted sentence is equivalent as the
following sql code:
begin;
> CREATE TABLE documents (
> docdesc text,
> misc text,
> modification_time timestamp with time zone DEFAULT now()
> );
> CREATE FUNCTION documents_update_mod_time() RETURNS trigger
> AS $$
> begin
> new.modification_time := now();
>
return new;
>
end
> $$
> LANGUAGE plpgsql;
> CREATE TRIGGER documents_modification_time
> BEFORE INSERT OR UPDATE ON documents
> FOR EACH ROW
> EXECUTE PROCEDURE documents_update_mod_time();
> commit;
>
as a non-native english speaker, I kind of feel this sentence quite hard to
understand....
