Issue if I replace merge with delete/insert? - sql-server

Question

I have this legacy code… Merge:
MERGE [Salesforce_Lead] AS target
using (
SELECT lead_id,
salesforce_id,
createdbyid,
email,
updatedate
FROM Source.Leads ) AS source
ON (
target.lead_id = source.lead_id)
WHEN matched
AND Checksum(target.lead_id, target.salesforce_id) <> Checksum(source.lead_id,source.salesforce_id)
OR Checksum(target.lead_id, target.createdbyid) <> Checksum(source.lead_id,source.createdbyid)
OR Checksum(target.lead_id, target.email) <> Checksum(source.lead_id,source.email)
OR Checksum(target.lead_id, target.updatedate) <> Checksum(source.lead_id,source.updatedate)
THEN
UPDATE
SET target.salesforce_id = source.salesforce_id,
target.createdbyid = source.createdbyid,
target.email = source.email,
target.updatedate = source.updatedate,
when not matched BY target THEN
INSERT
(
lead_id,
salesforce_id,
createdbyid,
email,
updatedate,
)
VALUES
(
source.lead_id,
source.salesforce_id,
source.createdbyid,
source.email,
source.updatedate
)
And I want to change it for the below code:
DELETE FROM [dbo].[Salesforce_Lead]
FROM [dbo].[Salesforce_Lead] AS L
INNER JOIN Source.Leads AS t
ON L.lead_id = t.lead_id;
INSERT INTO [dbo].[lead]
SELECT *
FROM Source.Leads
Reasons:
-shorter code, easier to maintain.
-I thought MERGE was supposed to be used if you were deleting from source as well, or using the OUTPUT clause…
-There are not many updates, usually is a plain insert.
Am I missing anything? the performance I would gain through the “when matched” is the only reason I should use MERGE, but as I said, most of them are inserts. Is there any issue if I replace merge with delete/insert?

Answer 1

The thing is that you can use merge statement to implement both initial and incremental loading. But if you want to use plain insert, sometimes it will be hard even if you just do the insert operation. Do you really want to truncate the target table first and then do the loading all over again every time you want to do the incremental load?
Another issue will be that if you are trying to implement as type-2 SCD, plain insert and update statement will be very complex and messy, however merge statement is very efficient and fast.