T-SQL Merge when matched not working - sql

Question

I have a temp table containing email traffic data between domains as follows:
[EmailId|SendingDomainId|SendingDomainName|RecipientDomainId|RecipientDomainName]
[500|600|abc.com|700|pqr.com]
[501|601|def.com|701|stu.com]
[501|601|def.com|700|pqr.com]
[502|600|abc.com|700|pqr.com]
That is:
email id 500 was sent from abc.com to pqr.com (1 sender, 1 recipient)
email id 501 was sent from def.com to stu.com and pqr.com (1 sender, 2 recipients)
email id 502 was sent from abc.com to pqr.com (1 sender, 1 recipient)
I am trying to compile a report which contains totals of emails sent between domains, to produce the following:
[SendingDomainId|SendingDomainName|RecipientDomainId|RecipientDomainName|Total]
[600|abc.com|700|pqr.com|2]
[601|def.com|701|stu.com|1]
[601|def.com|700|pqr.com|1]
I am trying this MERGE statement but the UPDATE part is not working. I am ending up with a final table containing the same rows as the source table.
MERGE #DomainsChord_TrafficData as T
USING #DomainsChord_DomainEmails AS S
ON (S.SendingDomainId = T.SendingDomainId AND
S.RecipientDomainId = T.RecipientDomainId)
WHEN MATCHED THEN UPDATE
SET T.TotalEmails = T.TotalEmails+1
WHEN NOT MATCHED BY TARGET THEN
INSERT (SendingDomainId, SendingDomainName, RecipientDomainId,
RecipientDomainName, TotalEmails)
VALUES (S.SendingDomainId, S.SendingDomainName,
S.RecipientDomainId, S.RecipientDomainName, 1);
Table #DomainsChord_TrafficData is an empty temp table before the merge. After the merge, it ends up with the same data as the source table (#DomainsChord_DomainEmails)
Is anyone able to spot where i am doing wrong?
Thanks in advance

Answer 1

If the table is empty before hand, then there is no Match for the update to execute, it is a NOT MATCHED and therefore the insert runs.

Answer 2

You don't need a MERGE in your case. You need a simple SELECT with a GROUP BY clause as follows:
SELECT SendingDomainId, SendingDomainName, RecipientDomainId, RecipientDomainName
, COUNT(*) AS Total
FROM #DomainsChord_DomainEmails
GROUP BY SendingDomainId, SendingDomainName, RecipientDomainId, RecipientDomainName;
OUTPUT
SendingDomainId SendingDomainName RecipientDomainId RecipientDomainName Total
--------------- ----------------- ----------------- ------------------- -----------
600 abc.com 700 pqr.com 2
601 def.com 700 pqr.com 1
601 def.com 701 stu.com 1
A MERGE statement is to merge data from two a source into a target. If your target (#DomainsChord_TrafficData) is empty, all data from source (#DomainsChord_DomainEmails) ends up in the target as you described.
Reference: MSDN MERGE T-SQL