Thank you Jeff, I was too sleepy to run comparison tests myself last night.

Your input length condition is a nice touch.

But no Jeff, it not a cross-join nor generates 65,536 internal rows. It's a n inner join. You can see it if you check out its execution plan, and it can be replaced with:

----------------------------------------

select @output = @output + char(b.dec)

from dec2hex a inner join dec2hex b

on b.hex = substring(@input,a.dec*2+1,2)

where a.dec*2+1 < LEN(@input)

order by a.dec

----------------------------------------

without affecting its semantics at all.

And dec2hex table is looked-up just LEN(@output) times.(It was 256 times before you add the criteria, though.)

I think it's weird that Richard's function is still much faster. I thought the join routine of the server should be most efficient. Moreover, my function calls substring() half the times of Richard's.

Anyway, it was a very interesting quiz. Thank you all!