>SQL Server has a varchar. There is a small amount of overhead associated with it, but it works very well.
>
>My two cents is that if the relationship is 1x1, I'd just add the column to the table.

I made a test locally. I added an integer field and a datetime field. This is 1.6 million records. They all have been initialized to 0 and the SQL Server empty date value. I stopped the SQL Server. I checked the disk. The size of all files did not change, not one single byte. The log, however, increased by 2 GB. I shrinked it after. It is back to 1 K.

So, it appears SQL Server reserves specific amount of space for things like this. Problably, something will start to grow in regards to this as the database is used.