销售出库单 下推 销售退货单，如何获知他们的关联关系?
T_SAL_OUTSTOCKENTRY 是销售出库单分录
T_SAL_RETURNSTOCKENTRY 是销售退货单分录
T_SAL_RETURNSTOCKENTRY_LK 是销售退货单单据关联配置表（关系表）
FSBILLID是源单ID，FSID是源分录ID
select T_SAL_OUTSTOCKENTRY.FREALQTY
,isnull(T_SAL_RETURNSTOCKENTRY.FREALQTY,0)
from T_SAL_OUTSTOCKENTRY
left join T_SAL_RETURNSTOCKENTRY_LK
on T_SAL_OUTSTOCKENTRY.FID = T_SAL_RETURNSTOCKENTRY_LK.FSBILLID
and T_SAL_OUTSTOCKENTRY.FENTRYID = T_SAL_RETURNSTOCKENTRY_LK.FSID
left join T_SAL_RETURNSTOCKENTRY
on T_SAL_RETURNSTOCKENTRY.FENTRYID = T_SAL_RETURNSTOCKENTRY_LK.FENTRYID
where T_SAL_OUTSTOCKENTRY.FID = 173384