<!--    跟据 指定字段 进行倒叙或者正序排序-->
    <select id="selectAll5" resultType="com.qfedu.entity.Student">
        select
        *
        FROM student s
        left join classgrade cc on s.id = cc.stuentId
        left join course cs on cs.gradeNum = cc.gradeNum order by

        <trim prefixOverrides="," suffixOverrides="">    <!-- prefix  插入指定字符，  prefixOverrides:指定去除多余的前缀内容 ， suffixOverrides:指定去除多余的后缀内容   -->
                    <if test="name == null  or  name ==''">
                        ,name asc
                    </if>
                    <if test="name != null  and  name !=''">
                        ,name desc
                    </if>


                    <if test="password != null  and  password !=''">
                        ,password desc
                    </if>

                    <if test="password == null  or  password ==''">
                        ,password asc
                    </if>
        </trim>
    </select>