MyBatis-

<?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="usernp">
<!--<sql>+<include> 查詢user表中id是1的記錄 -->
<sql id="columns">
id,name,addr,age
</sql>
<select id="findOne" resultType="User">
    select <include refid="columns"/> from user <where> id= #{id}</where>
</select>
<!-- if標籤-->
<select id="ifsql" resultType="User">
    select <include refid="columns"/> from user 
    <where> 
    <if test="id!=0">id=#{id}</if>
    <if test="name!=null">and name=#{name}</if>
    <if test="addr!=null">and addr=#{addr}</if>
    </where>
</select>
</mapper>

相應的測試類

 @Test
    public void ifSql() {
        // 2.建立SQLsession，執行SQL
        SqlSession session = ssf.openSession();
        // 第一個引數是sql的定位i，第二個是sql的引數值
        User user = session.selectOne("usernp.findOne", 1);
        // 3.處理結果
        System.out.println(user);
        // 4.釋放資源
        session.close();

    }