如何使用连接更新DB2表？

Posted 2021-04-15

我有两个表，我想通过加入它们来更新。我正在使用DB2 V9.7。

ORDER_APPROVALS

ORDER_ID    CREATED_BY_ID   CREATED_BY_NAME PROCESS_DT           
-------------------------------------------------------
234         2               admin           (null)    
307         2               admin           (null)    
313         2               admin           11-11-2013    

订单属性

ORDER_ID    ATTRIBUTE_ID    VALUE
-----------------------------------
234         123             ? --(ORDER_APPROVALS.CREATED_BY_NAME)
307         123             ? --(ORDER_APPROVALS.CREATED_BY_NAME)

我想针对Attribute_ID 123更新值字段。到目前为止，我尝试了以下查询。但这不起作用。我在Netezza尝试过类似的加入方式。想知道，如何在DB2中做到这一点？

update ORDER_ATTRIBUTE OT set OT.VALUE = 
(select CREATED_BY_NAME from ORDER_APPROVALS OA 
where OA.ORDER_ID = OT.ORDER_ID and OA.PROCESS_DT is NULL) 
where OT.ATTRIBUTE_ID = 123 and OT.ORDER_ID in 
(select ORDER_ID from ORDER_APPROVALS where PROCESS_DT is NULL)

答案

您正在寻找MERGE声明：

merge into ORDER_ATTRIBUTE ot
    using (select ORDER_ID, CREATED_BY_NAME
             from ORDER_APPROVALS
            where PROCESS_DT is null) oa
    on
       (ot.ORDER_ID = oa.ORDER_ID)
    when matched 
     and ot.ATTRIBUTE_ID = 123
    then update set VALUE = oa.CREATED_BY_NAME;

另一答案

我认为您需要使用派生表来完成此任务：

update order_attributes
set value = (
  select
  created_by_name
  from(    
    select
    created_by_name,
    oa.order_id
    from
    order_approvals oa
    left outer join order_attributes ot
    on oa.order_id = ot.order_id
    AND OT.ATTRIBUTE_ID = 123 
    and OT.ORDER_ID in 
      (select ORDER_ID from ORDER_APPROVALS where PROCESS_DT is NULL)
    ) ORDERS
 WHERE orders.order_id = order_attributes.order_Id
    )

另一答案

update ORDER_ATTRIBUTE OT set OT.VALUE = 
(select CREATED_BY_NAME from ORDER_APPROVALS OA 
where OA.ORDER_ID = OT.ORDER_ID and OA.PROCESS_DT is NULL) 
where OT.ATTRIBUTE_ID = 123 

这就够了。