Revert "Merge pull request rails#10710 from senny/5554_let_the_database_raise_on_counts"

This reverts commit b8e2978.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/lib/active_record/relation/calculations.rb

Reason: This change is not backward compatible and it was reverted
before 4.0.0 at 2ad168e so we can't include in 4-0-stable.

Closes rails#12417

Author: rafaelfranca

activerecord/CHANGELOG.md

@@ -196,22 +196,6 @@
 
     *Yves Senn*
 
-*   Remove column restrictions for `count`, let the database raise if the SQL is
-    invalid. The previos behavior was untested and surprising for the user.
-
-    Fixes #5554.
-
-    Example:
-
-        User.select("name, username").count
-        # Before => SELECT count(*) FROM users
-        # After => ActiveRecord::StatementInvalid
-
-        # you can still use `count(:all)` to perform a query unrelated to the
-        # selected columns
-        User.select("name, username").count(:all) # => SELECT count(*) FROM users
-
-    *Yves Senn*
 
 *   Fix the `:primary_key` option for `has_many` associations.
 

activerecord/lib/active_record/relation.rb

@@ -234,7 +234,7 @@ def size
     def empty?
       return @records.empty? if loaded?
 
-      c = count(:all)
+      c = count
       c.respond_to?(:zero?) ? c.zero? : c.empty?
     end
 

activerecord/lib/active_record/relation/calculations.rb

@@ -207,14 +207,15 @@ def perform_calculation(operation, column_name, options = {})
       end
 
       if operation == "count"
-        column_name ||= select_for_count
+        column_name ||= (select_for_count || :all)
 
         unless arel.ast.grep(Arel::Nodes::OuterJoin).empty?
           distinct = true
         end
 
         column_name = primary_key if column_name == :all && distinct
-        distinct = nil if column_name =~ /\s*DISTINCT[\s(]+/i
+
+        distinct = nil if column_name =~ /\s*DISTINCT\s+/i
       end
 
       if group_values.any?
@@ -378,9 +379,8 @@ def type_cast_using_column(value, column)
     # TODO: refactor to allow non-string `select_values` (eg. Arel nodes).
     def select_for_count
       if select_values.present?
-        select_values.join(", ")
-      else
-        :all
+        select = select_values.join(", ")
+        select if select !~ /[,*]/
       end
     end
 

activerecord/test/cases/calculations_test.rb

@@ -162,15 +162,6 @@ def test_no_limit_no_offset
     assert_no_match(/OFFSET/, queries.first)
   end
 
-  def test_count_on_invalid_columns_raises
-    e = assert_raises(ActiveRecord::StatementInvalid) {
-      Account.select("credit_limit, firm_name").count
-    }
-
-    assert_match "accounts", e.message
-    assert_match "credit_limit, firm_name", e.message
-  end
-
   def test_should_group_by_summed_field_having_condition
     c = Account.group(:firm_id).having('sum(credit_limit) > 50').sum(:credit_limit)
     assert_nil        c[1]