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我正在尝试在一个查询中执行计算，为计算值应用条件并计算结果。问题是我不知道如何从条件中引用计算字段。

我有 Issues.created_on 字段，我想查找有关在用户提供的几周内每周创建多少问题的统计信息。这是我的查询在 MySql 中的样子：

mysql>  SELECT status_id as group_id,
YEAR(created_on)*1000+WEEK(created_on,1) as range_value, count(*) as
noOfEntries FROM `issues` WHERE (`issues`.`project_id` IN (1))  GROUP
BY issues.status_id, range_value;

+----------+-------------+-------------+
| group_id | range_value | noOfEntries |
+----------+-------------+-------------+
|        1 |     2012031 |           2 |
|        5 |     2012015 |           1 |
+----------+-------------+-------------+

这是我的代码（简化）：

# Range value is dynamic: "YYYYXXX", where YYYY is year and XXX could be week, month or day of year
range_value = "YEAR(created_on)*1000+WEEK(created_on,1)"    
select = "#{range_value} as range_value, count(*) as noOfEntries"
grouping = "range_value"
# other conditions are provided by user, so we just add one here
conditions["range_value"] = range[:min]..range[:max]

rows = Issue.all(:select => select, :conditions => conditions, :readonly => true, :group => grouping)

但我得到这个错误：

ActiveRecord::StatementInvalid (Mysql::Error: Unknown column 'issues.range_value' in 'where clause': SELECT YEAR(created_on)*1000+WEEK(created_on,1) as range_value, 'weeks' as range_type, count(*) as logged_hours, 1 as entries, 'priority_id' as grouping, issues.priority_id as group_id FROM `issues` WHERE (`issues`.`range_value` BETWEEN '2012012' AND '2012031' AND `issues`.`project_id` IN (1))  GROUP BY range_value, issues.priority_id ORDER BY 1 asc, 6 asc):

我要修改的代码不是我的，所以我不能向 Issues 对象添加任何新字段或方法。所以像这样的解决方案对我不起作用，我猜。

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2 回答 2

0

你应该做这个：

rows = Issue.select(select).where(conditions).group(grouping).readonly

更清楚了。

于 2012-08-04T15:42:38.510 回答
0

我找到了一个实际上有帮助的代码示例：

ActiveRecord 没有用于在数据库查询中包含 HAVING 子句的参数，我有时发现自己需要它。幸运的是，您可以在 :group 参数的末尾偷偷添加它，而无需求助于 find_by_sql() 调用。（我不记得曾经在没有 GROUP BY 的情况下使用过 HAVING，尽管可能在某些情况下这样做是有意义的。）

例如，这是我的一个 Rails 应用程序的查询，它在数据库中查找所有重复的电子邮件地址：

duplicates = User.find( :all,
  :select     => "email, COUNT(email) AS duplicate_count",
  :conditions => "email IS NOT NULL AND email != ''",
  :group      => "email HAVING duplicate_count > 1"
)

因此，经过轻微修改，我的代码可以工作：

# Range value is dynamic: "YYYYXXX", where YYYY is year and XXX could be
# week, month or day of year
range_value = "YEAR(created_on)*1000+WEEK(created_on,1)"    
select = "#{range_value} as range_value, count(*) as noOfEntries"
# CHANGED THIS LINE from: grouping = "range_value"
grouping = " HAVING range_value BETWEEN #{range[:min]} AND #{range[:max]}"

# other conditions are provided by user, so we just add one here
# REMOVED THIS LINE
# conditions["range_value"] = range[:min]..range[:max]

rows = Issue.all(:select => select, :conditions => conditions, :readonly => true, :group => grouping)
于 2012-08-05T05:33:27.737 回答