Is it possible to have a primary key that increments by something other than a whole number? I'd like to create a table where the keys are all powers of 2, but I can't figure out how to make that work.

Go to the table design view. Highlight the primary key row in the designer. Look down at the bottom of that page and you'll see... Use identity seed and identity increment to define how the auto increment feature will work.

I get that they are there, but how would I say, "I want the next row to have a value of the 2 to the power of the last id"?

so you want the IDs to look like this:

2
4
8
16
32
etc.

An integer key that was incremented as a power of two would have very limited value. A mere 32 entries in the table would overflow an integer key: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048,
4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576,
2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728,
268435456, 536870912, 1073741824, 2147483648.

In a like manner - 64 entries would overflow a bigint key.


Rand

It's unlikely to ever get past 8-10. I appreciate the point, but I have a decent reason for wanting to do this.

Then you can just put those numbers in yourself. You probably won't get the DB to do it for you. But you could always increment the key yourself in the application.

By the way, I'm really interested to hear what your reason is for doing this.

Thanks. Best of luck with this.

Richard

Yeah, I just added another column that's computed as 2^(the key column), which will do. I was just trying to avoid the extra column. I'm using this to store permission information so I can figure out a user's rights quickly. See http://en.wikipedia.org/wiki/Bit_vector for a better explanation than I can give.

Thanks

Look up 'First Normal Form' to see why this may not be such a good idea...

Jeff Mason
Custom Apps, Inc.
www.custom-apps.com

Was it just that that was your 666th post or were you trying to be snide?