How to substract with no records

Question

hi all,
i have problem with substract value.
first table
code value corr
a 2 0.55
b 5 1
c 3 0.55
second table
code value corr
c 2 1
the result that i want is :
code value corr
a 2 0.55
b 5 1
c 1 0.55 --> from 3-2 and corr same like in table 1
c 2 1
i have tried with
select code, a.value - b.value value, a.corr
from table 1 a, table2 b
where a.code = b.code(+)
but the result is :
code val corr
a null 0.55
b null 1
c 1 0.55
would u suggest me what happened with this?
thanks all

Answer 1

select code, NVL(a.value,0) - NVL(b.value,0) value, a.corrUsing NVL may be give you the values for first two rows instead of null.
But on what logic do you get the second row here?
c 1 0.55
c 2 1