Question

我有一个带有表sentiment_records的ActiveRecord模型SentimentRecords，其中每条记录都有属性：user_id，sentiment_id，lecture_id和timestamp。我的查询：给定每个sentiment_id的LECTURE_ID和DATETIME，我想要计算每个sentiment_id记录了多少user_id（用户）;对于每个user_id，仅计算最新的时间戳＆lt; =给定的日期时间。

这是一个不起作用的配方：

SentimentRecords.find_by_sql
("SELECT sentiment_id,count(*) 
FROM sentiment_records WHERE id          
IN (SELECT max(id) FROM sentiment_records 
WHERE lecture_id=LECTURE_ID GROUP BY user_id 
WHERE timestamp <= DATETIME) GROUP BY sentiment_id")

Answer 1

我不确定我是否理解这些要求，但我认为你需要SQL就是这样的。

select s1.sentiment_id, count(s1.user_id)
from sentiment_records s1
inner join (
    select user_id, max(timestamp) as timestamp
    from sentiment_records
    where timestamp <= ?
      and lecture_id = ?
    group by user_id
    ) s2 on s1.user_id = s2.user_id and s1.timestamp = s2.timestamp
where lecture_id = ?
group by s1.sentiment_id;

Answer 2

这是正确的查询，感谢Nick Marden：

SentimentRecords.connection.select_all("SELECT sentiment_id, COUNT(*) FROM sentiment_records WHERE id IN (SELECT MAX(id) FROM sentiment_records WHERE lecture_id = LECTURE_ID AND timestamp < DATETIME GROUP BY user_id) GROUP BY sentiment_id")

用于Rails中复杂查询的正确SQL或ActiveRecord公式

2 个答案: