Projections / Arithmetic Operators

I've had a look at this patch (a little while ago now actually) and don't think it is ready for commit. Particularly it does not address what the correct return type of the projection should be. For example, the patch makes it possible to perform a binary operation (plus, minus, multiply or divide) on the values of two column projections, which could project columns of a different type. If one column is a decimal and the other an int, the code needs to derive an appropriate return type - in this case, a decimal to avoid any loss of precision.

Also from memory, I don't think GetTypes was implemented correctly: returning multiple types when a binary operator should only have one return type.

Thanks Onur! However, I am not a committer, so we have to wait for one to do this.

http://en.wikipedia.org/wiki/Committer

This looks pretty cool. Would you please commit this ?