29MyBatis - 动态SQL的 where标签

<!-- 根据条件查询用户 -->
<select id="queryUserByWhere" parameterType="user" resultType="user">
  SELECT id, username, birthday, sex, address FROM `user`
<!-- where标签可以自动添加where，同时处理sql语句中第一个and关键字 -->
  <where>
    <if test="sex != null">
      AND sex = #{sex}
    </if>
    <if test="username != null and username != ''">
      AND username LIKE
      '%${username}%'
    </if>
  </where>
</select>