MySQL的xml中对大于，小于，等于的处理转换
| 原符号 | < | <= | > | >= | & | ' | " |
| 替换符号 | < | <= | > | >= | & | ' | " |
例如：
<select id="select" parameterType="xxx" resultMap="xxx">
select
distinct
<include refid="Base_Column_List" />
from xxx
<where>
<if test="createDate != null">
create_date <= #{createDate}
</if>
</where>
</select>
