mybatis sql判断多个元素不为空

   SELECT * FROM result co
        where
        <if test="projectId != null">
             co.projectId=#{projectId} and
        </if>
        <if test="startTime!=null and endTime!=null">
        modifyTime between #{startTime} and #{endTime}
        </if>
        <if test="startTime!=null and endTime==null ">
         modifyTime>= #{startTime}
        </if>
        order by co.id desc;