[dspillett]

> Well MS SQL Merge statement is not very good

That is rather an understatement. IIRC unless you are careful with transaction isolation levels and other options, a single MERGE statement can still deadlock against itself.

See https://michaeljswart.com/2021/08/what-to-avoid-if-you-want-... and the older page it links to, mongst many references to the problems you can encounter.

Though things are a fair amount better than they used to be, back in 2008 when MERGE was first introduced, with most of the persistent buggy behaviours pertaining to specific features that not everyone uses, I still completely avoid it.