Question

我有3个表，item，item_cagegory和category。 Item和item_category在item_id中链接，item_category和category在category_id上链接。

我正在创建一个视图，列出类别的ID和名称，每个类别中的项目数，并计算该类别中所有项目的平均租金率。

我的所有代码似乎都有效，除了AVG_RATE似乎只是吐出了费率（而不是每个类别的平均费率）。有什么建议怎么做？

CREATE VIEW V_CATEGORY AS   
    SELECT DISTINCT category.category_id, category.name,
    (SELECT COUNT(*) FROM item_category 
        WHERE item_category.category_id = category.category_id) 
        AS items_in_category, 
    (SELECT AVG(item.rate) FROM item_category 
        WHERE item_CATEGORY.item_id = item.item_id 
        GROUP BY item_category.category_id) 
        AS avg_rate
        FROM category
    INNER JOIN item_category ON category.category_id = item_CATEGORY.category_id
    INNER JOIN item ON item_category.item_id = item.item_id;

Answer 1

尝试像这样编写select：

SELECT 
  category.category_id, 
  category.name,
  COUNT(item.item_id) as items_in_category,
  AVG(item.rate) as avg_rate
FROM
  category
INNER JOIN 
  item_category ON category.category_id = item_CATEGORY.category_id
INNER JOIN 
  item ON item_category.item_id = item.item_id
GROUP BY
  category.category_id, 
  category.name

带有COUNT，AVG列的Oracle SQL视图

1 个答案: