How to effeciently SELECT Nested dependency Tables using JOIN in SQL Server - sql

Question

I'm having One Parent Table "Employee", the Employee Information is stored in 3 Children Tables and each children table has one children Table. Consider the following Tables
Table : Employee (Level #1)
EmpId IsActive
__________________
1 1
2 1
3 1
4 0
5 0
6 1
Table : EmployeeEmail (Level #2)
EmpEmailId EmpId EmailId
______________________________
1 1 1
2 4 3
3 6 4
Table : EmailAddress (Level #3)
EmailId Email
____________________________
1 one#gmail.com
2 two#gmail.com
3 three#gmail.com
4 four#gmail.com
Table : EmployeePhone (Level #2)
EmpPhoneId EmpId PhoneId
______________________________
1 1 1
2 2 2
3 5 4
Table : PhoneNumber (Level #3)
PhoneId PhoneNumber
_______________________
1 9912345671
2 9912345672
3 9912345673
4 9912345674
Now I need to Select the Active Employee Records (Full Information), if the employee has phone number then it should come otherwise it should be NULL, I need the same for Email too.
Kindly assist me how to Join this structure and fetch the records efficiently ?

Answer 1

Try this query once it may help you.
select EMP.EmpId, EMP_ADD.Email,PH_NBR.PhoneNumber
from Employee EMP
LEFT JOIN EmployeeEmail EMP_EM ON EMP.EMP_ID=EmpId
LEFT JOIN EmailAddress EMP_ADD ON EMP_ADD.EmailId=EMP_EM.EmpEmailId
LEFT JOIN EmployeePhone EMP_PH ON EMP_PH.EmpId=EMP.EmpId
LEFT JOIN PhoneNumber PH_NBR ON PH_NBR.PhoneId=EMP_PH.PhoneId
WHERE EMP.IsActive=1
Note: Here i assume Active as 1 and Inactive as 0.in case if it is reverse then change where EMP.IsActive=0
(OR) Try this.here i'm trying to the phone and email data separately then joining them with emp_id
;with email as
(
select EMP.EmpId, EMP_ADD.Email
from Employee EMP
LEFT JOIN EmployeeEmail EMP_EM ON EMP.EMP_ID=EmpId
LEFT JOIN EmailAddress EMP_ADD ON EMP_ADD.EmailId=EMP_EM.EmpEmailId
WHERE EMP.IsActive=1
)
,Phone as
(
select EMP.EmpId,PH_NBR.PhoneNumber
from Employee EMP
LEFT JOIN EmployeePhone EMP_PH ON EMP_PH.EmpId=EMP.EmpId
LEFT JOIN PhoneNumber PH_NBR ON PH_NBR.PhoneId=EMP_PH.PhoneId
WHERE EMP.IsActive=1
)
select * from email e
left join Phone p on p.EmpId=e.EmpId

Answer 2

Alternative form:
only the three tables that you actually need are in the main query
the junction tables are used to glue them together via ON EXISTS(...):
SELECT e.empid, em.email, pn.phonenumber
FROM employee e
LEFT JOIN emailaddress em
ON EXISTS ( -- junctiontable
SELECT * FROM employeeemail ee
WHERE ee.empid = e.emp_id
AND ee.empemailid = em.emailid
)
LEFT JOIN phonenumber pn
ON EXISTS( -- junctiontable
SELECT * FROM employeephone ep
WHERE ep.empid = e.empid
AND ep.phoneid = pn.phoneid
)
WHERE e.isactive=1
;