CREATE TABLE public.t ( 
 f1 numeric(6,3),
 f2 numeric(6,4),
 f3 numeric(8,2)
) WITHOUT OIDS;


insert into public.t values ( 123.123, 12.1234, 12345.12);
insert into public.t values ( null, 12.1234, 12345.12);
insert into public.t values ( 123.123, null, 12345.12);
insert into public.t values ( 123.123, 12.1234, null);


--
--	Create sql text 
--

create view public v as 
select 
(f1+f2+f3) as fsum,
coalesce(f1,f2,f3) as fcoal,
(f1*f2*f3) as fprod
from public.t;

--
--	Parsed sql view from catalog
--

CREATE OR REPLACE VIEW public.v AS 
SELECT ((t.f1 + t.f2 ) + t.f3 ) AS fsum, 
        CASE WHEN (t.f1 IS NOT NULL ) THEN t.f1 
            WHEN (t.f2 IS NOT NULL ) THEN t.f2 
            WHEN (t.f3 IS NOT NULL ) THEN t.f3 
            ELSE NULL::numeric 
        END  AS fcoal, 
	((t.f1 * t.f2 ) * t.f3 ) AS fprod    FROM t;


--
--	Returned Data 
--

select * from public.v;

fsum		fcoal		fprod
12480.3664	123.123		18427182.594204384
null		12.1234		null			<< !!! No look good !!!
null		123.123		null
null		123.123		null


--
--
--	WORKAROUND WORKAROUND WORKAROUND
--
--

--
--	Create sql text with forced datatype
--

create view public v2 as 
select 
	cast( (f1+f2+f3) 		as dec(9,4) ) as fsum,
	cast( coalesce(f1,f2,f3)  	as dec(7,4) ) as fcoal,
	cast( (f1*f2*f3)  		as dec(20,9) ) as fprod
from public.t;

--
--	Parsed sql view from catalog
--

CREATE OR REPLACE VIEW public.v2 AS 
SELECT 
	(((t.f1 + t.f2 ) + t.f3))::numeric(9,4 ) AS fsum, 
	( CASE 
            WHEN (t.f1 IS NOT NULL ) THEN t.f1 
            WHEN (t.f2 IS NOT NULL ) THEN t.f2 
            WHEN (t.f3 IS NOT NULL ) THEN t.f3 
            ELSE NULL::numeric END)::numeric(7,4 ) AS fcoal, 
	(((t.f1 * t.f2 ) * t.f3))::numeric(20,9 ) AS fprod 
FROM t; 

--
--	Returned Data 
--

select * from public.v2;

fsum		fcoal		fprod
12480.3664	123.1230	18427182.594204384
null		12.1234		null			<< It's ok now
null		123.1230	null
null		123.1230	null