Select records when 2 column's data will match - sql-server

Question

I have two tables as shown below:
-----------------------
|EmpNo|Complaint |
-----------------------
|9091 |Change required|
|9092 |No change |
|9093 |Changes done |
-----------------------
Above table contains employee number and his complaints.
I have one another table which contains employee all kind of details as shown below.
-------------------------------
|EmpNo|EmailID |EmpBossNO|
-------------------------------
|9091 |abc#gmail.com|9092 |
|9092 |xyz#gmail.com|9093 |
|9093 |mno#gmail.com|9099 |
-------------------------------
Here, if Empno:9091 will raise any complain then a mail will send to his boss that the complain is raise by your employee and you have to accept it so I want to get EmailID of employee's boss and for that I want one SQL query. I tried the query shown here, but it doesn't work.
select EmpEmailID
from tblComplaint
inner join tblEmpMaster on tblEmpMaster.EmpNo = tblComplaint.EmpPSNo
where tblComplaint.EmpPSNo = tblEmpMaster.EmpBossNo
I want output like.. if complaint is raised by EmpNo:9091 then it will return EmailID of his boss which is xyz#gmail.com.

Answer 1

You are on the right track with a join between the tblComplaint and tblEmpMaster tables. But, you need an additional join to tblEmpMaster to bring in the boss' email for each employee complaint.
SELECT
c.EmpNo,
c.Complaint,
COALESCE(e2.EmailID, 'NA') AS boss_email
FROM tblComplaint c
INNER JOIN tblEmpMaster e1
ON c.EmpNo = e1.empNo
LEFT JOIN tblEmpMaster e2
ON e1.EmpBossNO = e2.EmpNo;
Demo
I used a left self join above, in case a given employee does not have a boss (e.g. for the highest ranking boss). In this case, I display NA for the boss email.

Answer 2

You should self join tblEmpMaster
select boss.EmpEmailID
from tblComplaint
inner join tblEmpMaster emp on emp.EmpNo = tblComplaint.EmpPSNo
inner join tblEmpMaster boss on boss.EmpNo = emp.EmpBossNO
where tblComplaint.EmpPSNo = 9091
DB Fiddle

Answer 3

you can even use sub queries to get the Email_Id of the boss as shown below
SELECT Email_Id
FROM EMP_Details
WHERE Emp_No IN (
SELECT Boss_Id
FROM Emp_Details) AND
Emp_No IN (
SELECT Emp_No
FROM Emp_Complaints)