Redshift SQL - 高/长到宽格式

Posted 2023-03-24

【中文标题】Redshift SQL - 高/长到宽格式

【英文标题】：Redshift SQL - Tall/long to Wide Format

【发布时间】：2021-12-07 02:59:33

【问题描述】：

我有一个名为“source_table”的表

|    Date    |  Country  | Subscribers |
----------------------------------------
| 2021-10-01 |    USA    |      5      |
| 2021-10-12 |  Canada   |      10     |
| 2021-10-23 |    USA    |      15     |
--
| 2021-11-01 |    USA    |      10     |
| 2021-11-05 |   Canada  |      20     |

我想把它转换成宽格式

| Country | Oct-21 | Nov-21 | Dec-21 |
--------------------------------------
|   USA   |   53   |   68   |   12   |
|  Canada |   35   |   86   |   21   |

我尝试了以下代码：

SELECT country,
       CASE WHEN date BETWEEN '2021-10-01' AND '2021-10-31' THEN SUM(subscribers)
       END AS "Oct-21",
       CASE WHEN date BETWEEN '2021-11-01' AND '2021-11-30' THEN SUM(subscribers)
       END AS "Nov-21",
       CASE WHEN date BETWEEN '2021-12-01' AND '2021-12-31' THEN SUM(subscribers)
       END AS "Dec-21"
FROM 
     source_table
GROUP BY 
     country

但是上面的代码抛出了一个错误提示

column "source_table.date" must appear in the GROUP BY clause or be used in an aggregate function

我不确定为什么 GROUP BY 中需要“日期”列；如果我确实在 GROUP BY 中使用它，我会让国家重复多次，这不是所需的输出。国家名称应该只出现一次，该月的订阅者数量汇总，并且列中不应有任何 NULL（source_table 中每个国家/地区每天至少有一个订阅者）。

我在这里遗漏了什么吗？请帮忙。我在 Redshift 上使用 SQL。

【参考方案1】：

您想对CASE 表达式求和或计数，例如

SELECT
    country,
    SUM(CASE WHEN date BETWEEN '2021-10-01' AND '2021-10-31'
             THEN subscribers ELSE 0 END) AS "Oct-21",
    SUM(CASE WHEN date BETWEEN '2021-11-01' AND '2021-11-30'
             THEN subscribers ELSE 0 END) AS "Nov-21",
    SUM(CASE WHEN date BETWEEN '2021-12-01' AND '2021-12-31'
             THEN subscribers ELSE 0 END) AS "Dec-21"
FROM source_table
GROUP BY country;

【讨论】：

已解决。谢谢。