SQL to append records

I have two tables tbl1 and tbl2. Consider tbl2 as the main set and tbl1 has been derived from other sources but will essentially now be a subset of tbl2.

tbl1

cd	productcd	type
1	1	A
1	2	AB
1	3	A
2	3	AB
2	4	AC
3	1	A

tbl2

cd	productcd	type	priority
1	1	A	1
1	2	AB	2
1	3	A	3
1	4	AB	4
1	5	AC	7
2	1	A	3
2	3	AB	4
2	4	AC	8
2	7	HV	10
3	1	A	2
3	2	AC	3
3	7	BC	5
3	4	E	9
3	5	T	11

How do I retrieve for each group of CD limit each group to only 4 records? So the final o/p has to be all the records of tbl1 and missing records ( max limit of 4) will be populated from tbl2

Final o/p being

cd	productcd	type
1	1	A
1	2	AB
1	3	A
1	4	AB
2	3	AB
2	4	AC
2	1	A
2	7	HV
3	1	A
3	2	AC
3	7	BC
3	4	E

Answer

If I understand correctly you can use row_number to select and order the required rows for each cd and use exists to prioritise rows from tbl1

with t as (
  select *, 
    Row_Number() over(
        partition by cd 
        order by 
            case when exists (
                    select * from tbl1 where tbl1.cd=tbl2.cd and tbl1.productcd=tbl2.productcd
                ) then 0 else 1 
            end, priority) rn
  from tbl2
)
select cd, productcd, type
from t
where rn<=4

See Working DB<>Fiddle