<!--声明一个SQL片段-->

<sql id="sql_findUserByifwhere">

    <where>

    <if test="user!=null and user!=''">

        <if test="user.sex!=null and user.sex!=''">

            sex=#{user.sex}

        </if>

        <if test="user.username!=null and user.username!=''">

            and username LIKE "%${user.username}%"

        </if>

    </if>

    </where>

</sql>

<select id="findUserByifwhere" parameterType="userQueryVO" resultMap="userByresultmap">

  select * from USER

    /*使用一个SQL片段*/

  <include refid="sql_findUserByifwhere"></include>

</select>