SQL How to create where clause to filter last six periods with this format YYYYMM : I want to run a query with a criteria that sums the previous 6 periods with the following period format yyyymm


    Period   Usage
    ======   =====
    201907   30
    201908   40
    201909   50
    201910   60
    201911   70
    201912   60
    202001   20