Alternative to SAS Merge

[Patrick]

Yes. If you run the sample code I've posted you'll see that it does.

[ChrisNZ]

You gave an example of id=50, which is new.
For so few transactions you can index the transactions. Or sorting them shouldn't take long anyway. Both methods work.
And the history table is always sorted with either method when you merge.

[ChrisNZ]

You'll need a composite index with ID and date.