Question

Is it possible to join on a field that isn’t in a table, but is derived from it?

For example, if I have one table mapping calendar dates to data, and another mapping days of the week (0-6) to data. How would one join the calendar dates table to the days of week table without adding a “day of week” field to the former?

Answer 1

try something like this:

select
    a.one+a.two, b.three
    from TableA           a
        inner join TableB b on a.one+a.two=b.three

just put your calculation in the join, index usage is unlikely though. you don’y say your database, but if you have some command to take the weekday() of the date, you can join on that:

inner join TableB on weekday(a.EventDate)=b.Weekday