sql - return a row of constant values if row does not exist

Question

I want to be able to return a row of none, none, 0 if no row is returned from query. I have this SQL:

select first, last, count(address)
from employee
where last in ('james', 'smith', 'hankers')
group by first, last
union all 
select 'none', 'none', 0
from dual
where not exists (select * from employee where last in ('james', 'smith', 'hankers'));

From DB, an entry for james and smith exists but no entry exists for hankers .

But this query only returns for when an entry exists. Does not return none, none, 0 .

What am I doing wrong here?

EDIT: In this example, I am passing 3 hard coded values as last , but I would like to know a work-around if we were passing the values in as a list parameter like so (:last) through getJdbcTemplate.

Answer 1

The NOT EXISTS is applied taking into consideration all of the values listed. So, if any one value exists then the NOT EXISTS is not satisfied.

As a work-around you can use an in-line table with the specified values and left join your original table to it:

select coalesce(t2.first, 'none'), 
       coalesce(t2.last, 'none'), 
       count(t2.address)
from (
   select 'james' as last
   union all
   select 'smith'
   union all
   select 'hankers') t1
left join employee t2 ON t1.last = t2.last
group by coalesce(t2.first, 'none'), 
         coalesce(t2.last, 'none')

If there is no match, as is the case for last='hankers' , then count(t2.address) evaluates to 0 and thus 'none', 'none', 0 is returned.

Answer 2

May this will help you,

_count NUMBER(10);

select count(*) into _count
from employee
where last in ('james', 'smith', 'hankers');

if(_count > 0)
then
   select first, last, count(address) c
   from employee
   where last in ('james', 'smith', 'hankers')
   group by first, last
else
   select 'none' first, 'none' last, 0 c   from dual
end if