Mybatis-Mapper.xml文件前缀详解

<?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="">
</mapper>

<sql id="Base_Column_List">
    id, question, answer 
  </sql>
  <select id="selectByPrimaryKey" parameterType="java.lang.Long" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from java
    where id = #{id,jdbcType=BIGINT}
  </select>

　<select id="selectByParams" parameterType="map" resultType="user">
　　　　select * from user
　　　　<where>
　　　　　　<if test="id != null ">id=#{id}</if>
　　　　　　<if test="name != null and name.length()>0" >and name=#{name}</if>
　　　　　　<if test="age != null and age.length()>0">and age = #{age}</if>
　　　　</where>
　　</select>　　　

　　<update>
　　　　update user 
　　　　<set>
　　　　　　	<if test="name != null and name.length()>0">name = #{name},</if>
　　　　　　	<if test="age != null and age .length()>0">age = #{age },</if>
　　　　</set>
　　　　where id = #{id}
　　</update>　

　　　select * from user 
　　<trim prefix="WHERE" prefixoverride="AND |OR">
　　　　<if test="name != null and name.length()>0"> AND name=#{name}</if>
　　　　<if test="age != null and age.length()>0"> AND age=#{age}</if>
　　</trim>

select * from user where name = ‘xx' and age = ‘xx'

　　update user
　　<trim prefix="set" suffixoverride="," suffix=" where id = #{id} ">
　　　　<if test="name != null and name.length()>0"> name=#{name} , </if>
　　　　<if test="age!= null and age.length()>0"> age=#{age} ,  </if>
　　</trim>

update user set name=‘xx' , age=‘xx' where id=‘x'

　<select id="selectByParams" parameterType="map" resultType="user">
　　　　select * from user where 1 = 1
　　　　　　  <choose>  
	            <when test="id !=null ">  
	                AND id = #{id}
	            </when >  
	            <when test="username != null and username != '' ">  
	                AND username = #{username}  
	            </when >  
	            <when test="age != null and age !=''">  
	                AND age = #{age}  
	            </when >  
	            <otherwise>  
	            </otherwise>  
       		 </choose>
　　</select>