Question

我的一个模型的命名范围很好。代码是：

named_scope :inbox_threads, lambda { |user|
{
  :include => [:deletion_flags, :recipiences],
  :conditions => ["recipiences.user_id = ? AND deletion_flags.user_id IS NULL", user.id],
  :group => "msg_threads.id"
}}

这在使用MySQL数据库的应用程序的本地副本上工作正常，但当我将我的应用程序推送到Heroku（仅使用PostgreSQL）时，我收到以下错误：

ActiveRecord::StatementInvalid (PGError: ERROR: column "msg_threads.subject" must appear in the GROUP BY clause or be used in an aggregate function:

SELECT "msg_threads"."id" AS t0_r0, "msg_threads"."subject" AS t0_r1, "msg_threads"."originator_id" AS t0_r2, "msg_thr eads"."created_at" AS t0_r3, "msg_threads"."updated_at" AS t0_r4, "msg_threads"."url_key" AS t0_r5, "deletion_flags"."id" AS t1_r0, "deletion_flags"."user_id" AS t1_r1, "deletion_flags"."msg_thread_id" AS t1_r2, "deletion_flags"."confirmed" AS t1_r3, "deletion_flags"."created_at" AS t1_r4, "deletion_flags"."updated_at" AS t1_r5, "recipiences"."id" AS t2_r0, "recipiences"."user_id" AS t2_r1, "recipiences"."msg_thread_id" AS t2_r2, "recipiences"."created_at" AS t2_r3, "recipien ces"."updated_at" AS t2_r4 FROM "msg_threads" LEFT OUTER JOIN "deletion_flags" ON deletion_flags.msg_thread_id = msg_threads.id LEFT OUTER JOIN "recipiences" ON recipiences.msg_thread_id = msg_threads.id WHERE (recipiences.user_id = 1 AND deletion_flags.user_id IS NULL) GROUP BY msg_threads.id)

我对Postgres的工作并不熟悉，那么我需要在这里添加什么才能使其工作？谢谢！

Answer 1

... must appear in the GROUP BY clause ...

MySQL公然违反标准，支持简单性，并允许您不在GROUP BY中指定您要查找的每一列，而是依赖于排序来选择“最佳”可用值。

另一方面，Postgres（以及大多数其他RDBMS）要求您为GROUP BY子句中选择的每一列命名。如果您手动汇编了该查询，则需要逐个将每列添加到GROUP BY中。如果ORM生成了该查询（基于所有双引号的内容），您将需要检查他们的Postgres支持和/或向他们提交错误。

MySQL到PostgreSQL和命名范围

1 个答案: