SELECT 中的子查询 - 来自外部查询的未分组列答案

【问题标题】：Sub query in SELECT - ungrouped column from outer querySELECT 中的子查询 - 来自外部查询的未分组列
【发布时间】：2020-11-01 00:13:26
【问题描述】：

我必须计算 ARPU（收入 / # 个用户），但出现此错误：

子查询使用来自外部查询的未分组列“usage_records.date” 第 7 行：在哪里 created_at

预期结果：

Revenue(day) = SUM(quantity_eur) 当天
用户数（天）= 当天之前注册的用户总数

Postgresql（查询）

SELECT 
    date_trunc('day', usage_records.date) AS day,
    SUM(usage_records.quantity_eur) as Revenue,
    ( SELECT 
        COUNT(users.id)
        FROM users 
        WHERE created_at <= date_trunc('day', usage_records.date)
    ) as users_count
    
FROM users 
INNER JOIN ownerships ON (ownerships.user_id = users.id) 
INNER JOIN profiles ON (profiles.id = ownerships.profile_id)
INNER JOIN usage_records ON (usage_records.profile_id = profiles.id)

GROUP BY DAY
ORDER BY DAY asc

【问题讨论】：

标签： postgresql

【解决方案1】：

您的子查询（对每一行执行）包含一个未在 group by 中提及但未参与聚合的列。这会产生错误但您也可以使用条件语句重构查询

SELECT 
    date_trunc('day', usage_records.date) AS day,
    SUM(usage_records.quantity_eur) as Revenue,
    sum( case when  created_at <= date_trunc('day', usage_records.date) 
        AND users.id is not null
        then 1 else 0 end ) users_count
    
FROM users 
INNER JOIN ownerships ON (ownerships.user_id = users.id) 
INNER JOIN profiles ON (profiles.id = ownerships.profile_id)
INNER JOIN usage_records ON (usage_records.profile_id = profiles.id)

GROUP BY DAY
ORDER BY DAY asc

【讨论】：