---
title: "Rails 5 solves ambiguous column issue"
description:
  "We now don't have to provide a table name in quoted string for fetching
  fields which are present in join table as well when used with group by clause"
canonical_url: "https://www.bigbinary.com/blog/rails-5-fixes-ambiguous-cloumn-name-for-projected-fields-in-group-by-query"
markdown_url: "https://www.bigbinary.com/blog/rails-5-fixes-ambiguous-cloumn-name-for-projected-fields-in-group-by-query.md"
---

# Rails 5 solves ambiguous column issue

We now don't have to provide a table name in quoted string for fetching fields
which are present in join table as well when used with group by clause

- Author: Abhishek Jain
- Published: July 21, 2016
- Categories: Rails 5, Rails

```ruby
users(:id, :name)
posts(:id, :title, :user_id)
comments(:id, :description, :user_id, :post_id)

>> Post.joins(:comments).group(:user_id).count
Mysql2::Error: Column 'user_id' in field list is ambiguous: SELECT COUNT(*) AS count_all, user_id AS user_id FROM `posts` INNER JOIN `comments` ON `comments`.`post_id` = `posts`.`id` GROUP BY user_id
```

As we can see `user_id` has conflict in both `projection` and `GROUP BY` as they
are not prepended with the table name `posts` in the generated SQL and thus,
raising SQL error `Column 'user_id' in field list is ambiguous`.

## Fix in Rails 5

This issue has been addressed in Rails 5 with
[this pull request](https://github.com/rails/rails/pull/21950).

With this fix, we can now `group by` columns having same name in both the
tables.

```ruby
users(:id, :name)
posts(:id, :title, :user_id)
comments(:id, :description, :user_id, :post_id)

>> Post.joins(:comments).group(:user_id).count
SELECT COUNT(*) AS count_all, "posts"."user_id" AS posts_user_id FROM "posts" INNER JOIN "comments" ON "comments"."post_id" = "posts"."id" GROUP BY "posts"."user_id"

=> { 1 => 1 }
```

This shows that now both `projection` and `Group By` are prepended with the
`posts` table name and hence fixing the conflict.

## Links

- [Human page](https://www.bigbinary.com/blog/rails-5-fixes-ambiguous-cloumn-name-for-projected-fields-in-group-by-query)