I have a date range - start date and ending date, which i have now got the number of days between them and now i need to multiply the number of days by the cost.

The problem is the cost is in a different table and when i do: days*availablerooms::Cost

nothing happens.

How can i do a calculation accross multiple tables??

any help would be much appreciated.

Is there a value in the "availableRooms::Cost" field? If you see none, this might be because there's no relation between the tables.

I seem to be experiencing the same type of problem.
Let me see whether el_pablo's solution does the trick....
Will revert....
:-)