如何合并来自不同表的具有相同名称但在SQL Server中具有不同值的两列

Question

I have three tables ( example ) STAFF, STU, EMP .

I want to combine the column EMPID in table STAFF and table EMP into 1 column?

My previous query is like this,

SELECT *
FROM STU s 
FULL OUTER JOIN STAFF st ON st.STAFFID = STUID 
FULL OUTER JOIN EMP e ON s.STUID = st.EMPID

The result is like this

The expected result is just like the above screenshot, but I want to join EMPID into one column only.

UPDATE :

I tried using this query:

SELECT 
    stu.stuid, stu.stuname, stu.stucode,
    s.staffid, s.staffname, s.staffcode,
    emp.empname, emp.empcode, 
    COALESCE (emp.empid, staff.staffid) AS col
FROM 
    STU, Staff, EMP 
FULL OUTER JOIN 
    STAFF s ON s.STAFFID = stu.STUID
FULL OUTER JOIN  
    EMP e ON stu.STUID = s.EMPID

but it displays an error like this

Answer 1

Use below query to get the desired result.

SELECT s.StuID, s.StuName, s.Stucode, st.StaffId, st.StaffName, st.Staffcode, isnull(st.EmpId, e.EmpId) EmpId, e.EmpCode, e.EmpName
FROM STU s FULL outer JOIN
     STAFF st
     ON st.STAFFID = STUID FULL OUTER JOIN
     EMP e
     ON s.STUID = st.EMPID

Note: You will get the one emp Id column as needed. If Staff emp id is not null then staff emp id will be displayed else employee emp id will be displayed