sql中的case when 语句详解

SELECT A.OrderSID as InvId,
E.BizInvType as TypeCode,
E.TypeName as TypeName,
B.SimpleName as CorpName,
C.StorName as StorName,
CASE
WHEN F_BS001QRYIONOTICE.UnitLevel_ = '1' THEN
-A.TotalDefQty / 250
WHEN F_BS001QRYIONOTICE.UnitLevel_ = '2' THEN
-A.TotalDefQty / 0
WHEN F_BS001QRYIONOTICE.UnitLevel_ = '3' THEN
-A.TotalDefQty
WHEN F_BS001QRYIONOTICE.UnitLevel_ = '4' THEN
-A.TotalDefQty * 10
WHEN F_BS001QRYIONOTICE.UnitLevel_ = '5' THEN
-A.TotalDefQty * 200
ELSE
-A.TotalDefQty
END as TotalDefQty,
A.DetailCount,
D.PersonName,
A.InputTime,
A.Remark,
F.Enterprise as Sourcename
FROM B_OD_OrderMaster A
INNER JOIN G_OG_CorpInfo B ON A.CorpSID = B.CorpSID
INNER JOIN B_ST_BSRealStorAttr C ON A.RealStorSID = C.StorSID
INNER JOIN G_OG_PersonInfo D ON D.PersonSID = A.InputOperSID
INNER JOIN G_PB_BizInvType E ON E.BizInvType = '02'
LEFT JOIN G_CS_CUSTOMER F ON A.CUSTOMERSID = F.CUSTOMERSID
WHERE A.IsActive = '1'
AND A.IsReturn = '1'
AND A.IsStorAudit = '0'
AND A.IsBizAudit = '0'
AND SUBSTR(A.InputTime, 1, 8) >= F_BS001QRYIONOTICE.BeginDate_
AND SUBSTR(A.InputTime, 1, 8) <= F_BS001QRYIONOTICE.EndDate_
AND A.CorpSID = (CASE WHEN F_BS001QRYIONOTICE.CorpSID_ = '' OR
F_BS001QRYIONOTICE.CorpSID_ IS NULL THEN A.CorpSID ELSE
F_BS001QRYIONOTICE.CorpSID_ END)
AND A.RealStorSID = (CASE WHEN F_BS001QRYIONOTICE.StorSID_ = '' OR
F_BS001QRYIONOTICE.StorSID_ IS NULL THEN
A.RealStorSID ELSE F_BS001QRYIONOTICE.StorSID_ END)
AND E.IsInStor =
(CASE WHEN F_BS001QRYIONOTICE.State_ = '1' THEN '1' ELSE E.IsInStor END)

AND E.IsOutStor =
(CASE WHEN F_BS001QRYIONOTICE.State_ = '2' THEN '1' ELSE E.IsOutStor END)