SQL---mybatis如何返回主键id

void add(@Param("user")User user);

<insert id="add" parameterType="com.java4all.User">
        <selectKey resultType="java.lang.String" order="AFTER" keyProperty="user.id">
            SELECT LAST_INSERT_ID()
        </selectKey>
        insert into user ( name, age,address)
        values ( #{user.name},#{user.age},#{user.address})
 </insert>

<insert id="add" parameterType="com.java4all.User" useGeneratedKeys="true" keyProperty="user.id">
        insert into user ( name, age,address)
        values ( #{user.name},#{user.age},#{user.address})
 </insert>

<insert id="add" parameterType="com.java4all.User" useGeneratedKeys="true" keyProperty="id">
        insert into user ( name, age,address)
        values ( #{name},#{age},#{address})
 </insert>