mybatis 在sql执行前，生成主键

  在insert中

   <selectKey keyProperty="useid" order="BEFORE" resultType="java.lang.String">

   SELECT UUID_SHORT() as   useid

  </selectKey>

 例如：

  <insert id="insert" parameterType="com.pojo.User" >

  <selectKey keyProperty="useid" order="BEFORE" resultType="java.lang.String">

   SELECT UUID_SHORT() as   useid

  </selectKey>

    insert into `user` (useid, username)

    values ( #{useid,jdbcType=VARCHAR} ,#{username,jdbcType=VARCHAR})

  </insert>