Sql server：连接两个表并使用子查询选择多个列值

Question

Table OpenPO

Shopping_Cart_No	Goods_Recipient_Emp_ID	accassgnmtownerid
1001958413	160213	65658
1001661570	61875	61855

Table Employee

employee_number	Email
160213	Quentin_Walker@gmail.com
61875	Mihaela_Balseanu@gmail.com
65658	siva@gmail.com
61855	mohan@gmail.com

I have these two tables, both are linked by the employee_number column.

I want to display data as shown below .

Expected result

Goods_Recipient_Email	Goods_Recipient_Emp_ID	accassgnmtownerid	accassgnmtownerid_Email
Quentin_Walker@gmail.com	160213	65658	siva@gmail.com
Mihaela_Balseanu@gmail.com	61875	61855	mohan@gmail.com

Tried with left join and able to compare and select only one email column Goods_Recipient_Emp_ID or op.accassgnmtownerid

SELECT 
    op.Goods_Recipient_Emp_ID, op.accassgnmtownerid, 
    te.Email AS accassgnmtownerid_Email
FROM 
    OpenPO op
LEFT JOIN 
    Employee te ON te.Employee_Number = op.Goods_Recipient_Emp_ID  

Tried with subquery for accassgnmtownerid_Email , but it didn't work out.

Can we apply subquery for accassgnmtownerid_Email or is there any other solution?

Answer 1

You need to join the table employee twice, using two different aliases.

For example:

select
  r.email as Goods_Recipient_Email,
  o.Goods_Recipient_Emp_ID,
  o.accassgnmtownerid,
  a.email as accassgnmtownerid_Email
from openpo o
join employee r on r.employee_number = o.Goods_Recipient_Emp_ID
join employee a on a.employee_number = o.accassgnmtownerid

Answer 2

Other than joining the tables for each Email, you can also use a correlated subquery for each, such as

select 
  (select Email from Employee e where e.employee_number = po.Goods_Recipient_Emp_ID) Goods_Recipient_Email,
  po.Goods_Recipient_Emp_ID,
  po.accassgnmtownerid,
  (select Email from Employee e where e.employee_number = po.accassgnmtownerid) accassgnmtownerid_Email
from OpenPO po;