I am currently using Tableau 8.2 and data views generated from MS Sequel.  I would like to chart current year vs. prior year or a specific year measure and calculation (i.e. current year vs. two years ago; current year vs. four years ago; two years ago vs. three years ago).  I'm being told this can only be done if the data in sequel is joined.  Is this correct or is there a calculation I can use?