跨表的SQL查询计算

SUM 分区依据 X_PO_NO . 使用 OVER 条款:

SELECT 
    b.[_PRESS_INST_NO]
    ,a.[X_PO_NO]
    ,a.[X_GOODS_CD]
    ,a.[X_QTY]
    ,c.RM_CD
    ,c.RM_QTY
    ,a.[X_QTY] * c.RM_QTY / 
    SUM(CAST(a.[X_QTY] AS float)) OVER (PARTITION BY a.X_PO_NO) AS RM_QTYPerUnit
FROM 
    T1 a
    INNER JOIN T2 b ON a.X_PO_NO=b.X_PO_NO
    INNER JOIN T3 c ON b._PRESS_INST_NO=c.[_PRESS_INST_NO]
;

X_QTY int ,然后将其投射到 float 或 decimal