prepend table name for `Relation#select` columns.

This fixes a bug where `select(:id)` combined with `joins()` raised:

```
ActiveRecord::StatementInvalid: SQLite3::SQLException: ambiguous column name: id:
SELECT  id, authors.author_address_id
FROM "posts"
INNER JOIN "authors"
ON "authors"."id" = "posts"."author_id"
ORDER BY posts.id LIMIT 3
```

The `select_values` are still String and Symbols because other parts (mainly calculations.rb)
rely on that fact.

/cc @tenderlove

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 9227c2b72f..e874c93110 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -1505,6 +1505,12 @@ class RelationTest < ActiveRecord::TestCase
     end
   end
 
+  test "joins with select" do
+    posts = Post.joins(:author).select("id", "authors.author_address_id").order("posts.id").limit(3)
+    assert_equal [1, 2, 4], posts.map(&:id)
+    assert_equal [1, 1, 1], posts.map(&:author_address_id)
+  end
+
   test "delegations do not leak to other classes" do
     Topic.all.by_lifo
     assert Topic.all.class.method_defined?(:by_lifo)