Don't preserve SELECT columns on COUNT

The COUNT clause of a finder_sql relationship is being rewritten from
COUNT(*) to COUNT(table_name.*). This does not appear to be valid syntax
in MySQL:

```
mysql> SELECT COUNT( table_name.* ) FROM `table_name`;
ERROR 1064 (42000): You have an error in your SQL syntax; check the
manual that corresponds to your MySQL server version for the right
syntax to use near '* ) FROM `table_name`' at line 1
```

This fixes the bug, as well as adding tests so we don't re-introduce
it in the future.

Fixes #3956.

2 files changed, 33 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index b15df4f308..babbb12e99 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -373,7 +373,8 @@ module ActiveRecord
             # replace the SELECT clause with COUNT(SELECTS), preserving any hints within /* ... */
             interpolate(options[:finder_sql]).sub(/SELECT\b(\/\*.*?\*\/ )?(.*)\bFROM\b/im) do
               count_with = $2.to_s
-              count_with = '*' if count_with.blank? || count_with =~ /,/
+              p count_with
+              count_with = '*' if count_with.blank? || count_with =~ /,/ || count_with =~ /\.\*/
               "SELECT #{$1}COUNT(#{count_with}) FROM"
             end
           end
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 04714f42e9..5edabb4790 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -46,10 +46,13 @@ class HasManyAssociationsTestForCountWithCountSql < ActiveRecord::TestCase
   end
 end
 
-class HasManyAssociationsTestForCountDistinctWithFinderSql < ActiveRecord::TestCase
+class HasManyAssociationsTestForCountWithFinderSql < ActiveRecord::TestCase
   class Invoice < ActiveRecord::Base
     ActiveSupport::Deprecation.silence do
       has_many :custom_line_items, :class_name => 'LineItem', :finder_sql => "SELECT DISTINCT line_items.amount from line_items"
+      has_many :custom_full_line_items, :class_name => 'LineItem', :finder_sql => "SELECT line_items.invoice_id, line_items.amount from line_items"
+      has_many :custom_star_line_items, :class_name => 'LineItem', :finder_sql => "SELECT * from line_items"
+      has_many :custom_qualified_star_line_items, :class_name => 'LineItem', :finder_sql => "SELECT line_items.* from line_items"
     end
   end
 
@@ -61,6 +64,33 @@ class HasManyAssociationsTestForCountDistinctWithFinderSql < ActiveRecord::TestC
 
     assert_equal 1, invoice.custom_line_items.count
   end
+
+  def test_should_count_results_with_multiple_fields
+    invoice = Invoice.new
+    invoice.custom_full_line_items << LineItem.new(:amount => 0)
+    invoice.custom_full_line_items << LineItem.new(:amount => 0)
+    invoice.save!
+
+    assert_equal 2, invoice.custom_full_line_items.count
+  end
+
+  def test_should_count_results_with_star
+    invoice = Invoice.new
+    invoice.custom_star_line_items << LineItem.new(:amount => 0)
+    invoice.custom_star_line_items << LineItem.new(:amount => 0)
+    invoice.save!
+
+    assert_equal 2, invoice.custom_star_line_items.count
+  end
+
+  def test_should_count_results_with_qualified_star
+    invoice = Invoice.new
+    invoice.custom_qualified_star_line_items << LineItem.new(:amount => 0)
+    invoice.custom_qualified_star_line_items << LineItem.new(:amount => 0)
+    invoice.save!
+
+    assert_equal 2, invoice.custom_qualified_star_line_items.count
+  end
 end
 
 class HasManyAssociationsTestForReorderWithJoinDependency < ActiveRecord::TestCase