1 files changed, 26 insertions, 7 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 4b13ac8be0..35b9ed4746 100755
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -437,18 +437,29 @@ module ActiveRecord
       end
 
       def change_column_default(table_name, column_name, default) #:nodoc:
-        current_type = select_one("SHOW COLUMNS FROM #{quote_table_name(table_name)} LIKE '#{column_name}'")["Type"]
+        column = column_for(table_name, column_name)
+        change_column table_name, column_name, column.sql_type, :default => default
+      end
+
+      def change_column_null(table_name, column_name, null, default = nil)
+        column = column_for(table_name, column_name)
+
+        unless null || default.nil?
+          execute("UPDATE #{quote_table_name(table_name)} SET #{quote_column_name(column_name)}=#{quote(default)} WHERE #{quote_column_name(column_name)} IS NULL")
+        end
 
-        execute("ALTER TABLE #{quote_table_name(table_name)} CHANGE #{quote_column_name(column_name)} #{quote_column_name(column_name)} #{current_type} DEFAULT #{quote(default)}")
+        change_column table_name, column_name, column.sql_type, :null => null
       end
 
       def change_column(table_name, column_name, type, options = {}) #:nodoc:
+        column = column_for(table_name, column_name)
+
         unless options_include_default?(options)
-          if column = columns(table_name).find { |c| c.name == column_name.to_s }
-            options[:default] = column.default
-          else
-            raise "No such column: #{table_name}.#{column_name}"
-          end
+          options[:default] = column.default
+        end
+
+        unless options.has_key?(:null)
+          options[:null] = column.null
         end
 
         change_column_sql = "ALTER TABLE #{quote_table_name(table_name)} CHANGE #{quote_column_name(column_name)} #{quote_column_name(column_name)} #{type_to_sql(type, options[:limit], options[:precision], options[:scale])}"
@@ -460,6 +471,7 @@ module ActiveRecord
         options = {}
         if column = columns(table_name).find { |c| c.name == column_name.to_s }
           options[:default] = column.default
+          options[:null] = column.null
         else
           raise ActiveRecordError, "No such column: #{table_name}.#{column_name}"
         end
@@ -536,6 +548,13 @@ module ActiveRecord
         def version
           @version ||= @connection.server_info.scan(/^(\d+)\.(\d+)\.(\d+)/).flatten.map { |v| v.to_i }
         end
+
+        def column_for(table_name, column_name)
+          unless column = columns(table_name).find { |c| c.name == column_name.to_s }
+            raise "No such column: #{table_name}.#{column_name}"
+          end
+          column
+        end
     end
   end
 end