select t1.f1,t2.f2
from t1 left join t2
where t1.f0=@value and t1.f0=t2.fx
或select t1.f1,t2.f2
from t1 right join t2
where t1.f0=@value and t1.f0=t2.fx
from t1 left join t2
where t1.f0=@value and t1.f0=t2.fx
或select t1.f1,t2.f2
from t1 right join t2
where t1.f0=@value and t1.f0=t2.fx
from t1 a left join t2 b
on a.f0=@value and a.f0=b.fx
但是出来的结果并不符合a.f0=@value 的条件,而是把整个t2 b都列出来了,不管是不是空
select a.f1,b.f2
from t1 a left join t2 b
on a.f0=b.fx
where a.f0=@value