bind例子：
num = num+1 例子
<bind name="num" value="0" />
<foreach collection="list" item="ss" index="index" separator=",">
<if test="ss.orderByField == 'soldAmount'">
<if test="ss.orderBy == -1">
<bind name="num" value="num+1" />
</if>
</if>
<if test="ss.orderByField == 'price'">
<if test="ss.orderBy == -1">
<bind name="num" value="num+1" />
</if>
</if>
</foreach>
<choose>
<when test="num==2">
and id=2
</when>
<otherwise>
and id=3
</otherwise>
</choose>
