Hello everyone, I am buiding up a database for activity school. Here first step of buiding the base, I got an attendance data type problem. i am now using "yes/no", but if i want to query about the number of student each class, is that possible?

Thank you for your help.

Yes is stored as -1 and No as 0. So if you do a sum on the yes/no field and remove the minus using Abs(), you have the total in attendance.

Thanks Neileg. So I can't use Yes/No, it is better to use 0 and 1?

sorry i am a newbie, i can see if i change the data type from "yes/no" into "number", it changes to -1 and 0. So I can calculate with "yes/no" type. Thanks!

The penny has dropped, I see!

The yes/no datatype isn't really a datatype at all. As you have seen, it's really a number. The same is true of the date/time. If you view it as a number, the date part is the integer and the time is the decimal fraction.

If you have studied languages that use the term CAST (or TYPECAST), then this statement will make sense to you.

Yes/No fields (a.k.a. Boolean when in VBA) are casts of type BYTE.

Date fields are casts of type DOUBLE.

Currency is a scaled cast of type OCTAWORD (which Access does not support as such, but supports the cast. Go figure.)