Question

我使用以下子句创建了一个表VQ1。

CREATE VIEW VQ1 as
SELECT productid, productname, TO_CHAR(unitprice,'$9,999.99') AS "unitprice"     
  FROM products
 WHERE unitprice > avg(unitprice) 
  WITH READ ONLY;

我收到错误消息，我无法使用汇总函数AVG()来查找平均值。

那么我怎样才能为视图找到AVG()？

Answer 1

你可以尝试这个伴侣：

CREATE VIEW VQ1 AS
SELECT
    productid,
    productname,
    TO_CHAR(unitprice, '$9,999.99') 'unitprice'
FROM
    products
GROUP BY
    productid
HAVING
    unitprice > AVG(unitprice);

Answer 2

因为avg是一个聚合函数，所以除非在group by子句中指定了其他字段，否则不能在select中使用它。

create view VQ1 as
select productid, productname, 
TO_CHAR(unitprice,'$9,999.99') as "unitprice" 
from products,
(select avg(unitprice) as avgprice from products)
where unitprice > avgprice
with read only;

Answer 3

您可以使用窗口（分析）函数完成此操作：

CREATE VIEW vq1 AS
SELECT productid, productname, unitprice FROM (
    SELECT productid, productname, unitprice, AVG(unitprice) OVER () AS avg_unitprice
      FROM products
) WHERE unitprice > avg_unitprice
  WITH READ ONLY;

无法在视图表中使用平均聚合

3 个答案: