求指点

select 
t1.*,t2.result
from t1
left join t2 on t1.uid=t2.uid
where t1.Class=1

if object_id('表一','U') is not null
   drop table 表一
go
create table 表一
(
 uId int,
 class char(10)
)
go
insert into 表一
select 1,1 union all
select 2,1 union all
select 3,1 union all
select 4,1 union all
select 5,1
go
if object_id('表二','U') is not null
   drop table 表二
go
create table 表二
(
 uid int,
 result int
) 
go
insert into 表二
select 1,10 union all
select 2,20
go

select a.uId,class,result = case when result is null then '没有' else cast(result as varchar) end from 表一 a left join 表二 b on a.uId=b.uId
/*
uId         class      result
----------- ---------- ------------------------------
1           1          10
2           1          20
3           1          没有
4           1          没有
5           1          没有

(5 行受影响)


*/

select 
t1.*,
result=isnull(result,'没有')
from t1
left join t2 on t1.uid=t2.uid
where t1.Class=1

/*
苦苦的潜行者
*/
if object_id('t1') is not null and object_id('t2') is not null
drop table t1,t2
create table t1 (uId int ,class char(2))
insert t1
select 1,'1' union all
select 2,'1' union all
select 3,'1' union all
select 4,'1' union all
select 5,'2'
create table t2 (uId int,result int)
insert t2
select 1,10 union all
select 2,20
go
select a.*,b.result from 
(select * from t1 where class='1') a 
left join t2 b on a.uId=b.uId
/*
（所影响的行数为 4 行）
uId  class result
---  -----  ----
1     1    10
2     1    20
3     1    null
4     1    null
*/
go 
drop table t1,t2

select uId, class,
(select result from 表二 where uId=a.uId) as result
from 表一 a 
where a.class='1'

select a.uid,a.class,case when isnull(b.result,0)=0 then '没有'else convert(char,b.result) end  as Result from t1 a left join t2 b  on a.uid=b.uid where a.class=1

select t1.*,case when t2.result is null then '没有' else t2.result end as result,
case when t2.result is null then '没有' else
dense_rank() over(order by t2.result) end as [rank]
from t1 left join t2 on t1.uid=t2.uid 
where t1.Class=1