select a.name, isnull(product,'없음'),  cast(isnull(b.countx,0) as char(3)) + '개'
from
tbl_area a left outer join
(
 select code, count(code) countx,
 min(
   case
   when product = '트럭' then '자동차'
   when product = '오리' then '자동차'
   else product
   end
 ) product
   
 from tbl_sale
 group by code
)b
on a.code = b.code

결과

name                                                                                                                 
---------- ---------------------------------------------------------------------------------------------------- -----
서울         자동차                                                                                                  3  개
경기         유모차                                                                                                  1  개
인천         없음                                                                                                   0  개
전남         없음                                                                                                   0  개
전북         없음                                                                                                   0  개
충남         없음                                                                                                   0  개
충북         없음                                                                                                   0  개
강원         없음                                                                                                   0  개
대구         없음                                                                                                   0  개
대전         없음                                                                                                   0  개
광주         없음                                                                                                   0  개
부산         없음                                                                                                   0  개