如何搜索SQL Server中发送的所有好友请求

Question

我需要SQL中的join帮助。我有2张桌子：

1. tbl_register
2. 请求

有一个问题：它只返回NULL中的req_from_id。

tbl_register表：

UserID     f_name      Designationnm    Comapny_name
1      aaa                 CEO              Apple
2      Rajeev      General manager          Dell
3      upendra     Managing director        Dell
4      soumendr        Vice president      lenovo
9      Suneal     Managing director        Apple
8       asa                CEO             Apple

request表：

req_from_id req_to_id   req_status
2              9               0
3              9               0
4              9               0
2              8               0
2              1               0

我需要得到这样的输出：

f_name       Designationnm   Comapny_name  UserID    req_from_id
aaa  aa             CEO            Apple     1             2
Rajeev          General manager    Dell      2             9
Suneal          Managing director  Apple     9             2
asa               CEO              Apple     8             2

我尝试过：

select distinct 
tb1.UserID,tb1.f_name,tb1.Designationnm,tb1.Comapny_name,tb2.req_from_id      
from Tbl_register tb1 
left join
tbl_friend_and_match_request tb2
on 
tb1.UserID = tb2.req_from_id
where 
Comapny_name like '%a%' or Designationnm like '%Manager%'

Answer 1

select   
tb1.UserID,tb1.f_name,tb1.Designationnm,tb1.Comapny_name,tb2.req_from_id      
from Tbl_register tb1 
left join
tbl_friend_and_match_request tb2
on tb2.req_to_id = tb1.userid
where company_name in ('Apple') or DesignationName in ('General manager')

Answer 2

SELECT tbl_register.f_name, 
  tbl_register.Designationnm, 
  tbl_register.Comapny_name, 
  tbl_registerUserID, 
  request.req_from_id 
FROM tbl_register
INNER JOIN request ON tbl_register.UserID=request.req_to_id  
GROUP BY tbl_register.UserID;