diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index 5358491cde..aaf9e2e73f 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -149,6 +149,10 @@ module ActiveRecord
         "INSERT INTO #{quote_table_name(table_name)} VALUES(DEFAULT)"
       end
 
+      def case_sensitive_equality_operator
+        "="
+      end
+
       protected
         # Returns an array of record hashes with the column names as keys and
         # column values as values.
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 35b9ed4746..204ebaa2e2 100755
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -511,6 +511,10 @@ module ActiveRecord
         keys.length == 1 ? [keys.first, nil] : nil
       end
 
+      def case_sensitive_equality_operator
+        "= BINARY"
+      end
+
       private
         def connect
           @connection.reconnect = true if @connection.respond_to?(:reconnect=)
diff --git a/activerecord/lib/active_record/validations.rb b/activerecord/lib/active_record/validations.rb
index 52f674847e..e7a9676394 100755
--- a/activerecord/lib/active_record/validations.rb
+++ b/activerecord/lib/active_record/validations.rb
@@ -627,17 +627,23 @@ module ActiveRecord
 
           is_text_column = finder_class.columns_hash[attr_name.to_s].text?
 
-          if !value.nil? && is_text_column
-            value = value.to_s
+          if value.nil?
+            comparison_operator = "IS ?"
+          else
+            comparison_operator = "#{connection.case_sensitive_equality_operator} ?"
+
+            if is_text_column
+              value = value.to_s
+            end
           end
 
+          sql_attribute = "#{record.class.quoted_table_name}.#{connection.quote_column_name(attr_name)}"
+
           if value.nil? || (configuration[:case_sensitive] || !is_text_column)
-            condition_sql = "#{record.class.quoted_table_name}.#{attr_name} #{attribute_condition(value)}"
+            condition_sql = "#{sql_attribute} #{comparison_operator}"
             condition_params = [value]
           else
-            # sqlite has case sensitive SELECT query, while MySQL/Postgresql don't.
-            # Hence, this is needed only for sqlite.
-            condition_sql = "LOWER(#{record.class.quoted_table_name}.#{attr_name}) #{attribute_condition(value)}"
+            condition_sql = "LOWER(#{sql_attribute}) #{comparison_operator}"
             condition_params = [value.downcase]
           end
 
@@ -654,28 +660,10 @@ module ActiveRecord
             condition_params << record.send(:id)
           end
 
-          results = finder_class.with_exclusive_scope do
-            connection.select_all(
-              construct_finder_sql(
-                :select     => "#{connection.quote_column_name(attr_name)}",
-                :from       => "#{finder_class.quoted_table_name}",
-                :conditions => [condition_sql, *condition_params]
-              )
-            )
-          end
-
-          unless results.length.zero?
-            found = true
-
-            # As MySQL/Postgres don't have case sensitive SELECT queries, we try to find duplicate
-            # column in ruby when case sensitive option
-            if configuration[:case_sensitive] && finder_class.columns_hash[attr_name.to_s].text?
-              found = results.any? { |a| a[attr_name.to_s] == value.to_s }
-            end
-            
-            if found
+          finder_class.with_exclusive_scope do
+            if finder_class.exists?([condition_sql, *condition_params])
               message = record.errors.generate_message(attr_name, :taken, :default => configuration[:message])
-              record.errors.add(attr_name, message) 
+              record.errors.add(attr_name, message)
             end
           end
         end