用空值替换/评估嵌套查询| Oracle SQL

我使用下面的查询，如果有点混乱，我很抱歉这是我得到这个结果的唯一方法：）但是在最左边的“PO”列中，当它全部完成时，有一个（null）的实例，请参见示例输出。这导致当我可以确认它们应该有值时，数值显示为（null）

我使用了NVL、NVL2、COALESCE函数，但没有成功

select query2.PO, query2.Work_Group, query2.PO_QTY_TO_Move, query8.Active_Pick_Faces AS Active_Pick_Faces, query4.C0R_Qty_To_Move AS Move_C0R, query6.NA_Qty_To_Move AS Move_NA
from((select PO, Work_Group, SUM(qty_to_move) AS PO_Qty_To_Move
        from(select order_header.purchase_order AS PO,order_header.work_group AS Work_Group, move_task.task_id, move_task.qty_to_move AS qty_to_move
                from order_header
                left join move_task
                on order_header.order_id = move_task.task_id
                where move_task.site_id = 'USCOL1' and move_task.client_id = 'SDRY-US' and move_task.status != 'Consol' )query1
        group by PO, Work_Group)query2
    left join
        (select PO, Work_Group, SUM(qty_to_move) AS C0R_Qty_To_Move
        from(select order_header.purchase_order AS PO,order_header.work_group AS Work_Group, move_task.task_id, move_task.from_loc_id, move_task.qty_to_move AS qty_to_move
                from order_header
                left join move_task
                on order_header.order_id = move_task.task_id
                left join location
                on move_task.from_loc_id = location.location_id
                where move_task.site_id = 'USCOL1' and move_task.client_id = 'SDRY-US' and location.work_zone = 'C0-R' and move_task.status != 'Consol' or order_header.purchase_order is null)query3
        group by PO, Work_Group)query4
    on query2.PO = query4.PO
    left join 
        (select PO, Work_Group, SUM(qty_to_move) AS NA_Qty_To_Move
        from(select order_header.purchase_order AS PO,order_header.work_group AS Work_Group, move_task.task_id, move_task.qty_to_move AS qty_to_move
                from order_header
                left join move_task
                on order_header.order_id = move_task.task_id
                where move_task.site_id = 'USCOL1' and move_task.client_id = 'SDRY-US' and move_task.from_loc_id like 'NA%' and move_task.from_loc_id not like '%PAL%' and move_task.status != 'Consol' )query5
        group by PO, Work_Group) query6
    on query2.PO = query6.PO
    left join 
        (select PO, Work_Group, SUM(qty_to_move) AS Active_Pick_Faces 
        from(select order_header.purchase_order AS PO,order_header.work_group AS Work_Group, move_task.task_id, move_task.qty_to_move AS qty_to_move
                from order_header
                left join move_task
                on order_header.order_id = move_task.task_id
                left join location
                on move_task.from_loc_id = location.location_id
                where move_task.site_id = 'USCOL1' and move_task.client_id = 'SDRY-US' and location.work_zone in ('C0S','C0S2','LAUNCH','C0-RPALLET', 'TRANSIT')and move_task.status != 'Consol' or move_task.from_loc_id like '%PAL%')query7
        group by PO, Work_Group) query8
    on query2.PO = query8.PO)

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您使用的连接条件如下：

on query2.PO = query8.PO

但null永远不等于（或不等于）任何其他值，因此如果

PO

为null，则不能使用相等检查；您需要使用

为null

。要同时检查这两个选项，可以执行以下操作：

on query2.PO = query8.PO
or (query2.PO is null and query8.PO is null)

---

.

要理解SQL为什么会这样做，您必须认识到null在SQL中表示未知，而不是什么都没有。我们不知道一个未知值是否与另一个未知值相同。因此null与null不匹配，

null=null

不正确且

null！=null

也不是真的。