可以使用窗口函数：

select worktype,
       (case when worktype = 'cars'
             then total + sum(case when worktype = 'variation' then total else 0 end) over ()
             when worktype = 'planes'
             then total - sum(case when worktype = 'variation' then total else 0 end) over ()
             else total
        end) as total
from t;

如果只有一排 'variation' ，也可以使用 join :

select t.worktype,
       (case when t.worktype = 'cars'
             then t.total + tv.total
             when t.worktype = 'planes'
             then t.total - tv.total 
             else t.total
        end) as total
from t join
     t tv
     on tv.worktype = 'variation'

不用看你的问题，我可以给你一个提示。
你喜欢：

SELECT (PLANES - VARIATION) AS PLANES,
    (CARS + VARIATION) AS CARS,
    BIKES,
    VARIATION
FROM (<YOUR MEGA QUERY WHICH MUST TO HAS [PLANES, CARS, BIKES, VARIATION]>)

也许您可以将其放入查询而不嵌套，但我看不到任何内容，我更希望在答案中确保。