When not to use surrogate primary keys?

Question

I have several database tables that just contain a single column and very few rows, often just an ID of something defined in another system. These tables are then reference

Answer 1

I would say the following criteria must be met:

• your natural key must be absolutely, positively, no-exceptions-allowed, unique (things like names, social security numbers etc. usually seem to be unique - but really aren't)

• your natural key should be as small as an INT, e.g. not significantly more than 4 bytes in size (don't use a VARCHAR(50) for your PK, and especially not for your clustering key in SQL Server !)

• your natural key ought to be stable, e.g. never change (OK, with ISO country codes, this is almost a given - except when countries like Yugoslavia or the USSR collapse, or other like the two Germanies unite - but that's rare enough)

If those conditions are met, you can consider a natural key as your PK - but that should be the 2% exception in all your tables - not the norm.