有以下三张表
主表：POHead
订单号 最后打印日期（任何订单行被打印后会更新此日期）
+-------+---------------------------+
| PONbr | PrintDateTime |
+-------+-------------------------+
| P001 | 2019-01-01 08:40:35.213 |
| P002 | 1900-01-01 00:00:00.000 |
| P003 | 2019-01-02 14:00:00.000 |
+-------+-------------------------+
PONbr 为主键
从表：PODet
订单号 订单行号 物品号 数量 行创建日期
+-------+---------+--------+-----+-------------------------+
| PONbr | LineNbr | ItemId | Qty | CreateDateTime |
+-------+---------+--------+-----+-------------------------+
| P001 | 1 | IT1 | 3 | 2019-01-01 08:00:00.000 |
| P001 | 2 | IT2 | 5 | 2019-01-01 08:00:00.000 |
| P002 | 1 | IT3 | 7 | 2019-01-01 08:00:00.000 |
| P002 | 2 | IT4 | 8 | 2019-01-01 08:00:00.000 |
| P003 | 1 | IT5 | 10 | 2019-01-02 08:00:00.000 |
| P003 | 2 | IT6 | 11 | 2019-01-03 08:00:00.000 |
+-------+---------+--------+-----+-------------------------+
PONbr、LineNbr 为联合主键
修改记录表：MdfLog
订单号 订单行号 修改时间 数量
+-------+---------+-------------------------+-----+
| PONbr | LineNbr | MdfDateTime | Qty |
+-------+---------+-------------------------+-----+
| P001 | 1 | 2019-01-01 08:00:00.000 | 3 |
| P001 | 2 | 2019-01-01 08:00:00.000 | 5 |
| P002 | 1 | 2019-01-01 08:00:00.000 | 7 |
| P002 | 2 | 2019-01-01 08:00:00.000 | 7 |
| P002 | 2 | 2019-01-01 10:00:00.000 | 8 |
| P003 | 1 | 2019-01-02 08:00:00.000 | 2 |
| P003 | 1 | 2019-01-02 18:00:00.000 | 10 |
| P003 | 2 | 2019-01-03 08:00:00.000 | 11 |
| P003 | 2 | 2019-01-04 08:10:00.000 | 12 |
+-------+---------+-------------------------+-----+
目标查询结果：
订单号 订单行号 是否需要打印（0 - 不需要；1 - 需要）
+-------+---------+-----------+
| PONbr | LineNbr | NeedPrin |
+-------+---------+-----------+
| P001 | 1 | 0 |
| P001 | 2 | 0 |
| P002 | 1 | 1 |
| P002 | 2 | 1 |
| P003 | 1 | 1 |
| P003 | 2 | 1 |
+-------+---------+-----------+
题目解释：
订单行记录（PODet）在新增或修改后会记录到 MdfLog 表中。
查询结果为列出所有订单行是否是需要打印状态。
“需要”打印的含义如下：
1. 订单从未被打印过
2. 订单行在打印后有过修改
3. 订单行是在最后一次打印后新增的
★最后一次修改后数量与最后一次打印时数量一致（修改回原来的数量），则不需要打印
select ph.PONbr as PONbr,pm.LineNbr as LineNbr,
(case when(MdfDateTime > PrintDateTime and pm.IsZero != 0 ) then 0 else 1 end) as NeedPrin
from POHead as ph
inner join (select ml.MdfDateTime,(ml.Qty - pd.Qty) as IsZero,pd.LineNbr,pd.PONbr from PODet as pd inner join MdfLog as ml on pd.PONbr = ml.PONbr and pd.LineNbr = ml.LineNbr) as pm on ph.PONbr = pm.PONbr