请教：一条sql不知道错在哪里

Question

select a.员工姓名,b.s,c.考核等级 from 员工名单表 as a,员工考核表 as c left join (select 员工ID,sum(差旅费) as s from 员工差旅费记录 group by 员工ID) as b on a.员工ID=b.员工ID where a.员工ID=c.员工ID

Answer 1

看下层级结构，from tbl1, tbl2 left join tbl3 必然有错。
可以改成：
select a.员工姓名,b.s,c.考核等级
from 员工名单表 as a
left join 员工考核表 as c
on a.员工ID=c.员工ID
left join (select 员工ID,sum(差旅费) as s
from 员工差旅费记录
group by 员工ID) as b
on a.员工ID=b.员工ID