Question

我在Ruby中有以下代码：

Comment.select("comments.*, COALESCE(SUM(votes.value), 0) AS rating,
  user_votes.value AS user_value").
  joins("LEFT JOIN votes ON votes.voteable_type = '"+type+"' AND votes.voteable_id = comments.id").
  joins("LEFT JOIN votes AS user_votes ON user_votes.voteable_type = '"+type+"' AND user_votes.voteable_id = comments.id AND user_votes.user_id = #{user_id}").
  where(conditions).group("comments.id").order("comments."+method).limit(limit).offset(offset)

当Rails生成此SQL查询时，它不包含完整的select语句：

SELECT COUNT(*) AS count_all, comments.id AS comments_id FROM `comments`
LEFT JOIN votes ON votes.voteable_type = 'reply' AND votes.voteable_id = comments.id 
LEFT JOIN votes AS user_votes ON user_votes.voteable_type = 'reply' AND 
user_votes.voteable_id = comments.id AND user_votes.user_id = 1 WHERE (commentable_id = 
1 AND commentable_type = 'Impression')
GROUP BY comments.id ORDER BY comments.rating DESC LIMIT 10 OFFSET 0

但是，如果我删除了group语句，那么它正确地包含了完整的select语句。发生了什么事？

Answer 1

选择语句中的注释。*与group by（“comments.id”）冲突。

所选的每列必须位于GROUP BY子句中，或者包含在聚合函数中。

SQL Server显示SQL错误：通过c.name

从tt_country c group中选择c。*

列'tt_country.country_id'在选择列表中无效，因为它不包含在聚合函数或GROUP BY子句中。

ActiveRecord和arel会抛出指定的select，因为它不明确/无效。

Rails：与GROUP BY结合使用时不会出现SQL SELECT语句

1 个答案: