SQL server CASE WHEN

CASE B.PARTS
                             WHEN '外框'
                             THEN ROUND(E.SpLength * E.pccd / 1000000, 3, 1)
                                  * B.sl
                             WHEN '内扇'
                             THEN ROUND(E.nsLength * E.nspccd / 1000000, 3, 1)
                                  * B.sl
                             WHEN '纱扇'
                             THEN ROUND(E.ssLength * E.sspccd / 1000000, 3, 1)
                                  * B.sl
                           END