pry(main)> Loan.joins(:statistics).where(state: <some states>).where.not(statistics: {state: <some other states>}).order(created_at: "desc").last.statistics.map(&:state)
2015-09-21 20:53:54,423|65310|DEBUG|development| - Loan Load (0.9ms) SELECT `loans`.* FROM `loans` INNER JOIN `statistics` ON `statistics`.`loan_id` = `loans`.`id` WHERE `loans`.`state` IN ('started', 'pending_declined') AND (`statistics`.`state` NOT IN ('prequalified', 'conditionally_approved', '4506t_results_uploaded', 'customer_forms_uploaded', 'ready_for_etran', 'etran_verified', 'forms_to_be_verified', 'forms_verified', 'credit_memo_entered', 'loandoc_generated', 'loandoc_completed', 'loandoc_customer_received_need_signatures', 'signatures_checked_and_uploaded', 'boarded')) ORDER BY `loans`.`created_at` ASC LIMIT 1
2015-09-21 20:53:54,426|65310|DEBUG|development| - Statistic Load (0.3ms) SELECT DISTINCT `statistics`.* FROM `statistics` WHERE `statistics`.`loan_id` = 97
=> ["started", "prequalified", "conditionally_approved", "customer_forms_uploaded", "ready_for_etran", "pending_declined"]
所以，也许我不明白这里发生了什么......我要求SQL找到一些他们的统计数据不包含某些值的贷款。在这个例子中，我想要遗漏任何统计为prequalified的贷款，但是，正如您从打印输出中看到的那样，贷款＃统计数据确实有prequalified以及其他几个我想退出。
有人可以对此有所了解吗？我已经和它斗了好几个小时了，我的脑袋正在旋转。
答案 0 :(得分：0)
因为你使用了last.statistics。这意味着贷款对象的结果将与统计数据结合，而您之前已创建条件。 查看您的上一个结果查询：
Statistic Load (0.3ms) SELECT DISTINCT `statistics`.* FROM `statistics` WHERE `statistics`.`loan_id` = 97
删除你的last.statistics
Loan.joins(:statistics).where(state: <some states>).where.not(statistics: {state: <some other states>}).order(created_at: "desc").map(&:state)
或
如果你想在map(&state)
Loan.joins(:statistics).where(state: <some states>).where.not(statistics: {state: <some other states>}).where("loans.id IN (97)").order(created_at: "desc")
答案 1 :(得分：0)
您查询返回longpress()和Loan的产品，因此它仍然会返回某些 Statistic但没有您的状态的Loan条记录指定。
如果您只希望Statistic在这些状态上没有Loan，那么您可能希望您的SQL成为这一行：
Statistic我的SQLfu并不是我引以为荣的，所以这可能不是最优化的查询，但它应该得到你期望的结果。
您可以将其转换为SELECT loans.*,
FROM loans
LEFT OUTER JOIN (
SELECT statistics.loan_id, COUNT(*) count
FROM quotes
WHERE statistics.state IN ('prequalified', 'conditionally_approved')
GROUP BY statistics.loan_id
) statistics
ON statistics.loan_id = loans.id
WHERE loans.state IN ('started', 'pending_declined')
AND statistics.count IS NULL;
查询界面，但不幸的是，子查询和ActiveRecord实际上并不受支持，至少不是我们要使用它的方式将是这样的：
LEFT JOIN如果您不熟悉join_query = <<SQL
LEFT OUTER JOIN (
SELECT statistics.loan_id, COUNT(*) AS count
FROM statistics
WHERE statistics.state IN (<<state>>)
) statistics ON loans.id = statistics.loan_id
SQL
Loan
.joins(join_query)
.where(statistics: { count: null })
.where(state: <<somestate>>)
.order(created_at: :desc)
，则<<SQL ... SQL为Heredoc。