标签：
１．动态SQL基本标签
•if
•choose (when, otherwise)
•trim (where, set)
•foreach
２．IF 具体用法
<select id="XX"
resultType="Blog">
SELECT * FROM BLOG
WHERE state = ‘ACTIVE’
<if test="title != null">
AND title like #{title}
</if>
</select>
多个IF注意第二个ｉｆ语句里的表达式
<select id="XX"
resultType="Blog">
SELECT * FROM BLOG WHERE state = ‘ACTIVE’
<if test="title != null">
AND title like #{title}
</if>
<if test="author != null and author.name != null">
AND author_name like #{author.name}
</if>
</select>
３．类似 if ,else用法例子
<select id="XX"
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>
4．Where用法例子
<select id="XX"
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>
</select>
<select id="XX"
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>
6．trim用法
<trim prefix="WHERE" prefixOverrides="AND |OR "> ... </trim>
７．set用法注意set是sql语句中update table set.....不是将一个参数set到一个属性中
<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>
8.foreach用法
<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>
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原文地址：http://www.cnblogs.com/maybo/p/5183585.html
