Mapper.xml
//查詢總記錄數
<select id="getPagerList" parameterType="java.util.Map" resultMap="map">
    SELECT
    <choose>
        <!--查詢總記錄數-->
        <when test="iscount!=null and iscount!=''">
            COUNT(*) id
        </when>
        <otherwise>
            c.*,
            cs.name as cname,
            i.realname as iname,
            s.realname as sname
        </otherwise>
    </choose>
    FROM comment c
    LEFT JOIN course cs ON cs.id = c.cid
    LEFT JOIN instructor i ON i.id = c.iid
    LEFT JOIN student s ON s.id = c.sid
    WHERE 1=1

    <if test="cid != null and cid != ''">
        AND c.cid like concat('%', #{cid}, '%')
    </if>
    <if test="iid != null and iid != ''">
        AND c.iid like concat('%', #{iid}, '%')
    </if>
    <if test="sid != null and sid != ''">
        AND c.sid like concat('%', #{sid}, '%')
    </if>

<!--條件查詢-->
<select id="getAllWhere" parameterType="java.util.Map" resultMap="map">
    SELECT
        c.*,
        cs.name as cname,
        i.realname as iname,
        s.realname as sname
    FROM comment c
    LEFT JOIN course cs ON cs.id = c.cid
    LEFT JOIN instructor i ON i.id = c.iid
    LEFT JOIN student s ON s.id = c.sid
    WHERE 1=1

    <if test="cid != null and cid != ''">
        AND c.cid like concat('%', #{cid}, '%')
    </if>
    <if test="iid != null and iid != ''">
        AND c.iid like concat('%', #{iid}, '%')
    </if>
    <if test="sid != null and sid != ''">
        AND c.sid like concat('%', #{sid}, '%')
    </if>
</select>

<resultMap id="map" type="cn.educate.model.commentModel" autoMapping="true">
    <association property="course" javaType="cn.educate.model.courseModel">
        <result property="name" column="cname" />
    </association>
    <association property="instructor" javaType="cn.educate.model.instructorModel">
        <result property="realname" column="iname"/>
    </association>
    <association property="student" javaType="cn.student.model.studentModel">
        <result property="realname" column="sname"/>
    </association>
</resultMap>