这可以通过条件聚合来完成（假设每个代码的每个id有一行）。

select id 
      ,coalesce(max(case when code = 'code1' then cast(amount as int) end), 0) -
       coalesce(max(case when code = 'code2' then cast(amount as int) end), 0) +
       coalesce(max(case when code = 'code3' then cast(amount as int) end), 0) -
       coalesce(max(case when code = 'code4' then cast(amount as int) end), 0) 
from tbl
group by id