fix default select when from is used

activerecord/CHANGELOG.md

+*   Improve the default select when from is used.
+
+    Previously, if you did something like Topic.from(:temp_topics), it
+    would generate SQL like:
+
+      SELECT topics.* FROM temp_topics;
+
+    Which is useless, cause obviously there's not a topics table to select
+    from. So one would always have to include a select to override the
+    default behavior. Now the default if you use from is just *:
+
+      SELECT * FROM temp_topics;
+
+    Which may not be what you want in all cases, but is at least usable
+    in some cases.
+
+    *Cody Cutrer*
+
 *   Fix `PostgreSQL` insert to properly extract table name from multiline string SQL.
 
     Previously, executing an insert SQL in `PostgreSQL` with a command like this:

activerecord/lib/active_record/relation/query_methods.rb

@@ -982,8 +982,10 @@ def build_joins(manager, joins)
     end
 
     def build_select(arel, selects)
-      unless selects.empty?
+      if !selects.empty?
         arel.project(*selects)
+      elsif from_value
+        arel.project(Arel.star)
       else
         arel.project(@klass.arel_table[Arel.star])
       end

activerecord/test/cases/relations_test.rb

@@ -151,6 +151,11 @@ def test_finding_with_subquery_with_binds
     assert_equal relation.to_a, Comment.select('a.*').from(relation, :a).to_a
   end
 
+  def test_finding_with_subquery_without_select
+    relation = Topic.where(:approved => true)
+    assert_equal relation.to_a, Topic.from(relation).to_a
+  end
+
   def test_finding_with_conditions
     assert_equal ["David"], Author.where(:name => 'David').map(&:name)
     assert_equal ['Mary'],  Author.where(["name = ?", 'Mary']).map(&:name)