SQL Server : UPSERT transaction not reaching insert - sql

Question

Browsing on various examples on how to create a "good" UPSERT statement shown here, I have created the following code (I have changed the column names):
BEGIN TRANSACTION
IF EXISTS (SELECT *
FROM Table1 WITH (UPDLOCK, SERIALIZABLE), Table2
WHERE Table1.Data3 = Table2.data3)
BEGIN
UPDATE Table1
SET Table1.someColumn = Table2.someColumn,
Table1.DateData2 = GETDATE()
FROM Table1
INNER JOIN Table2 ON Table1.Data3 = Table2.data3
END
ELSE
BEGIN
INSERT INTO Table1 (DataComment, Data1, Data2, Data3, Data4, DateData1, DateData2)
SELECT
'some comment', data1, data2, data3, data4, GETDATE(), GETDATE()
FROM
Table2
END
COMMIT TRANSACTION
My problem is, that it never does the INSERT part. The INSERT alone works fine. The current script only does the update part.
I have an idea that the insert is only good, if it can insert the entire data it finds (because of the select query)? Otherwise it won't work. If so, how can I improve it?
I have also read about the MERGE clause and would like to avoid it.
//EDIT:
After trying out few samples found on the internet and explained here, I re-did my logic as follows:
BEGIN TRANSACTION
BEGIN
UPDATE table1
SET something
WHERE condition is met
UPDATE table2
SET helpColumn = 'DONE'
WHERE condition is met
END
BEGIN
INSERT INTO table1(data)
SELECT data
FROM table2
WHERE helpColumn != 'DONE'
END
COMMIT TRANSACTION
When trying other solutions, the INSERT usually failed or ran for a long time (on a few tables, I can accept it, but not good, if you plan to migrate entire data from one database to another database).
It's probably not the best solution, I think. But for now it works, any comments?

Answer 1

Instead of
if (something )
update query
else
insert query
Structure your logic like this:
update yourTable
etc
where some condition is met
insert into yourTable
etc
select etc
where some condition is met.

Answer 2

You cannot check this in general, like you are doing. You have to check each ID from Table 2 if it exists in Table 1 or not. If it exists, then update Table 1 else insert into Table 1. This can be done in following way.
We are going to iterate on Table 2 for each ID using CURSORS in SQL,
DECLARE #ID int
DECLARE mycursor CURSOR
FOR
SELECT ID FROM Table2 FORWARD_ONLY --Any Unique Column
OPEN mycursor
FETCH NEXT FROM mycursor
INTO #ID
WHILE ##FETCH_STATUS = 0
BEGIN
IF EXISTS (SELECT 1 FROM Table1 WHERE ID = #ID)
UPDATE t1 SET t1.data= T2.data --And whatever else you want to update
FROM
Table1 t1
INNER JOIN
Table2 t2
ON t1.ID = t2.ID --Joining column
WHERE t1.id = #ID
ELSE
INSERT INTO Table1
SELECT * FROM Table2 WHERE ID = #ID
FETCH NEXT FROM mycursor
INTO #ID
END
CLOSE mycursor
DEALLOCATE mycursor