this has nothing to do with SQL Server. on SQL Server MERGE is atomic, if the source has no indexes it's probably a temp table, of course evaluating "not matche

this has nothing to do with SQL Server. on SQL Server MERGE is atomic, if the source has no indexes it's probably a temp table, of course evaluating "not matched" requires joining the source to the target, on SQL Server you should be thinking and working in sets and avoiding single row (RBAR) whenever possible. if you're doing highly concurrent single-row upserts you're already SQL Servering wrong and I'll concede that's a case where you probably need a bunch of lock hints (regardless if it's a merge statement or an update followed by an insert)