適用於Rails中復雜查詢的正確SQL或ActiveRecord公式

Question

我有一個帶有表sendiment_records的ActiveRecord模型SentimentRecords，其中每個記錄都具有以下屬性：user_id，sentiment_id，lecture_id和時間戳。 我的查詢：給定一個LECTURE_ID和一個DATETIME，對於每個sentiment_id，我想要一個計數來記錄每個sendiment_id的user_id的數量。 對於每個user_id，僅計算最新時間戳<=給定日期時間。

這是無效的公式：

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

我不確定我是否理解要求，但是我認為您需要類似這樣的SQL。

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

感謝Nick Marden，這是正確的查詢：

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")