7 . 动态sql-choose

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>