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