这样的语句怎们能优化一下,现在发现数据量大的时候很慢

[Oo云]

select case when jvolum.jiayoujiaci is null then j.jjiayou else j.jjiayou - jvolum.jiayoujiaci*2 end as '加油架次',
j.jyue as '月份', j.jgongjin as '加油量(吨)' from (select 
datepart(mm,BSTDK) as jyue, 
count(BSTKD) as jjiayou,
sum(KWMENG)/1000 as jgongjin
from 
jiayoudan
where datepart(YYYY,BSTDK) = @year
group by datepart(mm,BSTDK)) AS j 
left join (select 
datepart(mm,BSTDK) as yue, 
count(BSTKD) as jiayoujiaci
from jiayoudan
where VOLUM = 0 and datepart(YYYY,BSTDK) = @year
group by datepart(mm,BSTDK)) AS jvolum on j.jyue = jvolum.yue
order by '月份'

[--小F--]

把你第一个表里面的嵌套部分拿出来写在一个临时表里面

select
datepart(mm,BSTDK) as jyue,
count(BSTKD) as jjiayou,
sum(KWMENG)/1000 as jgongjin
from
jiayoudan
where datepart(YYYY,BSTDK) = @year
group by datepart(mm,BSTDK)

[--小F--]

然后在没有函数的连接部分加索引