How to show all categories by joining the two table and display 0 if category not existed?

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I have tbl1 and tbl2

tbl1:

id Service
==================
1 Microsoft
2 Oracle
3 Java

tbl2

Service RollNumber
==========================
Microsoft 13
Microsoft 12
Java 2
Java 16
Microsoft 15

How can i get as below using linq:

Service Counts
===================
Microsoft 3
Java 2
Oracle 0

What I have tried:

var data = from t1 in tbl1
join t2 in tbl2
on t1.Service.Trim() equals t2.Service.Trim() into eGroup
from t2in eGroup.DefaultIfEmpty()

Posted 19-Sep-18 19:13pm

shaprpuff

Updated 19-Sep-18 23:34pm

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OriginalGriff · Answer 1 · 2018-09-19T19:52:00

You are doing that wrong: tbl2 should contain the ServiceID, not the name:

ServiceID RollNumber
1          13
1          12
3           2
3          16
2          15

And use a JOIN to access the Service name.

That does make the final query you want slightly more complex, but not a lot:

SELECT a.Service, ISNULL(b.CNT, 0) 
FROM tbl1 a
LEFT JOIN (SELECT ServiceID, COUNT(RollNumber) AS CNT 
           FROM tbl2
           GROUP BY ServiceID) b 
       ON a.ID = b.ServiceID

And do yourself two favours:
1) Use sensible table names! It makes your queries so much more readable, and thus reliable...
2) Add an IDENTITY id column to tbl2, to prevent duplication. You don't need to use it in most of your queries, but SQL will not allow you to have duplicate rows.

Maciej Los · Answer 2 · 2018-09-19T23:35:00

Try this:

C#

var data = from t1 in tbl1
    join t2 in tbl2 on t1.Service.Trim() equals t2.Service.Trim() into eGroup
    from together in eGroup.DefaultIfEmpty()
    select new 
    {
       Service = together.?Service,
       Count = together.Count()
    };

For further details, please see: Perform left outer joins (LINQ in C#) | Microsoft Docs[^]

Another way is to calculate count of records in a table #2 based on service name:

C#

var result = tbl1
	.Select(x=> new
	{
		Service = x.Service,
		Count = tbl2.Count(y=> y.Service.Trim()==x.Service.Trim()))
	});

Good luck!

How to show all categories by joining the two table and display 0 if category not existed?

2 solutions

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