Question

我有如下查询：

Author.select('authors.*, max(books.published_at) as last_publishing')
  .joins(:books)
  .group('authors.id')

这就是我想要的（返回用最近发布日期注释的作者列表），但是如果我尝试对此查询调用count，则会出现问题。

SELECT COUNT(authors.*, max(books.published_at) as last_publishing) 
AS count_authors_all_max_books_published_at_as_last_publishing, authors.id 
AS authors_id FROM "authors"
INNER JOIN "books"
ON "books"."author_id" = "authors"."id"
GROUP BY authors.id

*** ActiveRecord::StatementInvalid Exception: PG::SyntaxError: ERROR:  syntax error at or near "as"
LINE 1: ...COUNT(authors.*, max(books.published_at) as last_pu...

显然这不是我想要生成的SQL - 我只想要一个SELECT COUNT（*）FROM（）myQuery。

我看到有a similar issue with Rails 4 - 还有其他人反对这个/是否有解决方法？我可以做query.to_a.size，但我更愿意能够为我和我的同事使用count方法，未来的理智。

Answer 1

您应该在呼叫计数

之前删除select temporary

authors = Author.select('authors.*, max(books.published_at) as last_publishing')
      .joins(:books)
      .group('authors.id')
    total_authors = authors.except([:includes]).count(:all)

计数在Rails中使用聚合函数失败

1 个答案: