mybaties mapping中if..else

<select id="selectSelective" resultMap="xxx" parameterType="xxx">
    select
    <include refid="Base_Column_List"/>
    from xxx
    where del_flag=0
    <choose>
        <when test="xxx !=null and xxx != ''">
            and xxx like concat(concat('%', #{xxx}), '%')
        </when>
        <otherwise>
            and xxx like '**%'
        </otherwise>
    </choose>
</select>