How to get one to many relationship data? - sql

Question

These are two tables having one-to-many relationship:
Employee[Table]:
---------------------------------------------------
EmpId | Name | Country | Salary | Email
--------------------------------------------------
1 John USA 875847 john#test.com
2 Mike USA 785487 mike#test.com
Lincense[Table]
----------------------------------------
EmpId | LicenseType | LincenseNumber
----------------------------------------
1 LincenseType1 12345678
1 LincenseType2 87654321
1 LincenseType3 78945613
2 LincenseType1 12345678
2 LincenseType2 87654321
2 LincenseType3 78945613
EmployeeDetails[Expected ResulSet]
-----------------------------------------------------------------------------------------------
EmpId | Name | Country | LicenseType | LicenseNumber | Salary | Email
-----------------------------------------------------------------------------------------------
1 John USA LincenseType1 12345678 875847 john#test.com
LincenseType2 87654321
LincenseType3 78945613
2 Mike USA LincenseType1 12345678 785487 mike#test.com
LincenseType2 87654321
LincenseType3 78945613
----------------------------------------------------------------------------------------------
To get result in above expected format what would be the best way to achieve that so that result contain only one row for Employee detail and all associated License details?

Answer 1

This here will do the trick for you. Remember if your empid and salary are int columns you can only null them or set 0 into it. Otherwise it need to be of type string
SQL Code
declare #emp table (empid int,[name] nvarchar(50),Country nvarchar(50),Salary int,[Email] nvarchar(50)
)
insert into #emp
values
(1 ,'John', 'USA', 875847, 'john#test.com'),
(2 ,'Mike', 'USA', 785487, 'mike#test.com')
declare #lic table (empid int, licensetype nvarchar(50),licencenumber int)
insert into #lic
values
(1 ,'LincenseType1', 12345678),
(1 ,'LincenseType2', 87654321),
(1 ,'LincenseType3', 78945613),
(2 ,'LincenseType1', 12345678),
(2 ,'LincenseType2', 87654321),
(2 ,'LincenseType3', 78945613)
select
empid = case when rn > 1 then null else x.empid end,
[name] = case when rn > 1 then '' else [name] end,
Country = case when rn > 1 then '' else country end,
licensetype = licensetype,
licencenumber = licencenumber,
Salary = case when rn > 1 then '' else Salary end,
Email = case when rn> 1 then '' else Email end
from (
select a.empid,[name],country,licensetype,licencenumber,Salary,Email,ROW_NUMBER() over(partition by a.empid order by licensetype) as rn from #emp a left join #lic b on a.empid = b.empid
)x
SQL Update
If Lincencetype should always be 1 on first row you can just do it like this. This will be faster
select
empid = case when licensetype !='LincenseType1' then null else a.empid end,
[name] = case when licensetype !='LincenseType1' then '' else [name] end,
Country = case when licensetype !='LincenseType1' then '' else country end,
licensetype = licensetype,
licencenumber = licencenumber,
Salary = case when licensetype !='LincenseType1' then '' else Salary end,
Email = case when licensetype !='LincenseType1' then '' else Email end
from #emp a inner join #lic b on a.empid = b.empid
Result

Answer 2

How about this?
SELECT Employee.EmpId, Employee.Name, Employee.Country,
Lincense.LicenseType, Lincense.LincenseNumber,
Employee.Salary, Employee.Email
FROM Employee JOIN Lincense
ON (Employee.EmpId = Lincense.EmpId);
If you are looking for empty values as you have shown, the best approach is to do that in your reporting tool rather than trying to do that in SQL

Answer 3

This is not what you want but close enough:
SELECT A.EMPID, A.NAME, A.COUNTRY, STUFF((SELECT ','+ b.LicenseType FROM License b WHERE A.EMPID = B.EMPID FOR XML PATH('')),1,1,'') AS LicenseType, STUFF((SELECT ','+ C.LicenseNumber FROM License C WHERE A.EMPID = C.EMPID FOR XML PATH('')),1,1,'') AS LicenseNumber, A.Salary, A.Email
FROM Employee A
It will not give you blank rows but will put LicenseType and LicenseNumber in same columns delimited by commas.

Answer 4

SELECT Employee.EmpId, Employee.Name, Employee.Country,
Lincense.LicenseType, Lincense.LincenseNumber,
Employee.Salary, Employee.Email
FROM Employee
JOIN Lincense ON Employee.EmpId = Lincense.EmpId;
Will give you simmilar result but all rows will be filled with data.
SELECT Employee.EmpId, Employee.Name, Employee.Country,
Lincense.LicenseType, Lincense.LincenseNumber,
Employee.Salary, Employee.Email
FROM Employee
LEFT OUTER JOIN Lincense ON Employee.EmpId = Lincense.EmpId;
Will give you result for all employees, even if it has no licence, you will notice those rows by having nulls on Lincence's properties
SELECT Employee.EmpId, Employee.Name, Employee.Country,
Lincense.LicenseType, Lincense.LincenseNumber,
Employee.Salary, Employee.Email
FROM Employee
RIGHT OUTER JOIN Lincense ON Employee.EmpId = Lincense.EmpId;
Will give you result for all licences, even if employee is not present, you will notice those rows by having nulls on Employee's properties
If you need the empty rows, it's bad practice to do that in DB. Handle that in backend code once you obtain result. Or even only when displaying the result in front end.
NOTE it's Licence or License, depending in what English you prefer.