<select id="selectByExampleExt" parameterType="com.cn21.redisCluster.model.AppInfoExampleExt" resultMap="BaseResultMapExt">        SELECT temp.*,r.* from (            SELECT a.* from appinfo as a where 1=1             <if test="appid != null and appid != ‘‘ ">                and a.appid=#{appid,jdbcType=VARCHAR}            </if>            <if test="productid != null">                and a.productid=#{productid,jdbcType=INTEGER}            </if>            ORDER BY a.lastupdatetime DESC            <if test="limitStart&gt;=0 and limit&gt;0">   （这里就是类似的 <if test="limitStart>=0 and limit>0">）                LIMIT ${limitStart} , ${limit}            </if>            <if test="limitStart==-1 and limit&gt;0">                LIMIT ${limit}            </if>             ) temp,redisdb r where temp.appid = r.appid    </select>