Nice question.

It made me think, briefly, because I was startled by the unnamed single column constraint. I'm so used to writing unnamed single column primary key, unique, reference, and check constraints (and of course default constraints, but they are inherently single column anyway) as part of the column definition that seeing one written elsewhere was a surprise; but after a very rapid reflection realised that as the syntax is available for (unnamed) multicolumn constraints there's no reaon it can't be used for (unnamed) single column constraints as an alternative to including the constraint in the column definition.

From the discussion I learnt that named constraints are allowed on temp tables; that is really awful - table variables have this one right.