MyBatis的动态SQL语句实现

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.joker.dao.IUserDao">
 
 <select id="findByUser" resultType="user" parameterType="user">
 select * from user where 1=1
 <if test="username!=null and username != '' ">
  and username like #{username}
 </if>
 <if test="address != null">
  and address like #{address}
 </if>
 </select>
</mapper>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.joker.dao.IUserDao">
 
 <select id="findByUser" resultType="user" parameterType="user">
 select * from user
 <where>
  <if test="username!=null and username != '' ">
  and username like #{username}
  </if>
  <if test="address != null">
  and address like #{address}
  </if>
 </where>
 </select>
</mapper>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.joker.dao.IUserDao">
 
 <!-- 查询所有用户在 id的集合之中 
 foreach标签：用于遍历集合
  * collection：代表要遍历的集合元素，注意编写时不要写 #{}
  * open：代表语句的开始部分
  * close：代表结束部分
  * item：代表遍历集合的每个元素，生成的变量名
  * sperator：代表分隔符
 -->
 <select id="findInIds" resultType="user" parameterType="queryvo">
 select * from user
 <where>
  <if test="ids != null and ids.size() > 0">
  <foreach collection="ids" open="id in ( " close=")" item="uid" separator=",">
   #{uid}
  </foreach>
  </if>
 </where>
 </select>
</mapper>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.joker.dao.IUserDao">
 
 <!-- 抽取重复的语句代码片段 -->
 <sql id="defaultSql">
 select * from user
 </sql>

 <select id="findAll" resultType="user">
 <include refid="defaultSql"></include>
 </select>
 
 <select id="findById" resultType="User" parameterType="int">
 <include refid="defaultSql"></include>
 where id = #{uid}
 </select>

</mapper>