choose-when-otherwise
只能满足一个when 中的条件，互斥的条件，不能同时存在
mapper.xml
<select id="selectstateByTitleOrstyle" parameterType="Blog" resultMap="blogResultMap" >
select * from blog where state = "1"
<choose>
<when test="title != null and title != ''">
and title like #{title}
</when>
<when test="style != null and style != ''">
and style = #{style}
</when>
<otherwise>
and featured = "1"
</otherwise>
</choose>
</select>
实际应用：
<choose>
<when test="page !=null and page.orderBy != null and page.orderBy != ''">
ORDER BY ${page.orderBy}
</when>
<otherwise>
ORDER BY a.update_date DESC
</otherwise>
</choose>