code: function update() {
      var updateData = this._prepUpdate(this.single.update);
      var wheres = this.where();
      var returning = this.single.returning;
      return {
        sql: 'update ' + this.tableName + ' set ' + updateData.join(', ') + (wheres ? ' ' + wheres : '') + this._returning(returning),
        returning: returning
      };
    }
docs: Compiles the "update" query.