用SQL填充SQL中的字段

Question

我有一个SQL查询，提供品牌名称和订单计数（案例1）。

我必须准备一份每小时的报告，但如果我没有为任何品牌计算一小时，则不会显示特定品牌（案例-2）。

在这种情况下，我如何在警报邮件中自动填充brand2？

示例SQL

SELECT distinct(brand), count(*) Hourly Count
FROM table_name where date_time between systimestamp-1/24 and systimestamp
GROUP BY brand;

Answer 1

首先，几乎不需要使用select distinct和group by（当然，在这种情况下，一列不必要地被括号括起来）并且显示对两种结构都缺乏了解。

执行所需操作的一种方法是使用条件聚合：

SELECT brand,
       SUM(CASE WHEN date_time between systimestamp-1/24 and systimestamp THEN 1 ELSE 0 END) as HourlyCount
FROM table_name 
GROUP BY brand;

另一种方法假设您有一个包含所有品牌的表格：

SELECT b.brand, count(t.brand) as HourlyCount
FROM brands b LEFT JOIN
     table_name 
     ON b.brand = t.brand AND
        t.date_time between systimestamp-1/24 and systimestamp
GROUP BY b.brand;

Answer 2

请找到我想要的内容。

SELECT DISTINCT(BRAND_NAME),SUM(COUNT)FROM(
    SELECT distinct(BRAND_NAME) ,count(*) COUNT
    FROM TABLE
    UNION ALL
      SELECT BRAND_NAME,0 AS COUNT
    FROM (SELECT 'Brand1' AS BRAND_NAME FROM DUAL 
    UNION ALL
    SELECT 'Brand2' AS BRAND_NAME FROM DUAL 
    UNION ALL
    SELECT 'Brand3' AS BRAND_NAME FROM DUAL)
    TEMP1)
    TEMP2
    GROUP BY BRAND_NAME
    ORDER BY 1;