标签：拼接 语句 update type author color style err ati
动态sql是mybatis的特色功能，所谓动态sql,就是支持sql语句的动态拼接，从而使sql语句的使用更加灵活，使代码简洁可复用。
以下就常用的动态sql用法做一些总结。
<select id="findActiveBlogWithTitleLike" resultType="Blog"> SELECT * FROM BLOG WHERE state = ‘ACTIVE’ <if test="title != null"> AND title like #{title} </if> </select>
<select id="findActiveBlogLike" resultType="Blog"> SELECT * FROM BLOG WHERE state = ‘ACTIVE’ <choose> <when test="title != null"> AND title like #{title} </when> <when test="author != null and author.name != null"> AND author_name like #{author.name} </when> <otherwise> AND featured = 1 </otherwise> </choose> </select>
3.trim where set 智能得插入 where and set ,等关键字，注意where与and配合使用，而set与，配合使用
<select id="findActiveBlogLike" resultType="Blog"> SELECT * FROM BLOG <where> <if test="state != null"> state = #{state} </if> <if test="title != null"> AND title like #{title} </if> <if test="author != null and author.name != null"> AND author_name like #{author.name} </if> </where> </select>
<trim prefix="WHERE" prefixOverrides="AND |OR "> ... </trim>
<update id="updateAuthorIfNecessary"> update Author <set> <if test="username != null">username=#{username},</if> <if test="password != null">password=#{password},</if> <if test="email != null">email=#{email},</if> <if test="bio != null">bio=#{bio}</if> </set> where id=#{id} </update>
<trim prefix="SET" suffixOverrides=","> ... </trim>
4.foreach 遍历集合参数
<select id="selectPostIn" resultType="domain.blog.Post"> SELECT * FROM POST P WHERE ID in <foreach item="item" index="index" collection="list" open="(" separator="," close=")"> #{item} </foreach> </select>
标签：拼接 语句 update type author color style err ati
原文地址：http://www.cnblogs.com/swaggyC/p/6115119.html
