Question

有人可以给我一个使用视图作为关系的查询示例吗？或者如何将此查询作为关系转换为视图？

SELECT COUNT(Y.custorderID) AS NoOfOrders, x.city ||' '||
       EXTRACT(YEAR FROM TO_DATE(Y.dateorderplaced, 'DD-MON-RR'))
FROM (SELECT custorderid, custID, customerorder.dateorderplaced
      FROM CustomerOrder
      WHERE EXTRACT(MONTH FROM
            TO_DATE(CustomerOrder.dateorderplaced, 'DD-MON-RR')) =1 AND  EXTRACT(YEAR FROM
      TO_DATE(CustomerOrder.dateorderplaced, 'DD-MON-RR')) = 2017
     )  Y
     INNER JOIN Customer x
         ON Y.custID = x.custID
GROUP BY x.city, y.dateOrderplaced

Answer 1

Create view getProducts_v as (
  SELECT * 
  FROM  Product
  WHERE Active = 'Y' and OnHandQty>0);

SELECT * 
FROM  GetProducts_v P
INNER JOIN  ProductCategory PC
 on PC.ProductID = P.ID
WHERE PC.Name in ('Houseware','Kitchen')

视图getProducts_v仅提供活动的项目列表以及存在的可用性。

然后，查询使用该视图获取家庭用品厨房中仅有这些产品的列表。由于视图已经过滤掉了非活动状态和那些具有0 onHandQty的视图，我们只向用户显示我们拥有的活动和活动状态。

拿走你拥有的东西：

CREATE view GetOrderHeader_v as (
      SELECT custorderid, custID, customerorder.dateorderplaced
      FROM CustomerOrder
     );

SELECT COUNT(gOH.custorderID) AS NoOfOrders
     , x.city ||' '||  EXTRACT(YEAR FROM TO_DATE(gOH.dateorderplaced, 'DD-MON-RR')) 
FROM  GetOrderHeader_v gOH
INNER JOIN Customer x
   ON gOH.custID = x.custID
WHERE EXTRACT(MONTH FROM TO_DATE(gOH.dateorderplaced, 'DD-MON-RR')) =1 
  AND EXTRACT(YEAR FROM TO_DATE(gOH.dateorderplaced, 'DD-MON-RR')) = 2017
GROUP BY x.city ||' '||  EXTRACT(YEAR FROM TO_DATE(Y.dateorderplaced, 'DD-MON-RR')) 
       , gOH.dateOrderplaced;

注意如果字段已经是日期数据类型，我将不会使用上面的to_date，因为它会增加不必要的开销。如果dateorderplaced还没有日期，我会对表格结构有所顾虑。

通常我只会在复杂查询中使用这样的视图，或者我想在逻辑中包含一个表以消除冗余检查;比如我们只展示活跃的产品;但我们不会从产品表中删除产品，因此我们让开发人员参考GetProducts_v，它永远不会显示已删除的产品或缺货产品。

将视图用作关系的查询

1 个答案: