<select id="" parameterType="Map"   resultMap="commodityResultMap" >        SELECT c.id c_id,c.variety_id,c.nickName c_nickName,c.description c_description,c.ordinaryPrice c_ordinaryPrice,c.memberPrice c_memberPrice,c.path c_path,v.id v_id,v.nickName v_nickName         FROM commodity c         INNER JOIN variety v         ON c.variety_id=v.id         where 1=1                       <!-- _parameter.containsKey(‘键‘) 作用：判断键是否存在返回值boolean  #{键}取对应的值   ！必须三处键值对应，否则取不到值-->             <if test="_parameter.containsKey(‘varietyID‘)">                 and v.id=#{varietyID}             </if>    </select>

• 此做法的好处，可做多条件查询。