sql一对多的查询代码怎么查？
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参考技术A代码如下：
SELECT a.trumbnail, b.url, c.url
FROM Goods a, Picture b, Picture c
WHERE a.picture=b.id AND a.picture=c.id
参考技术Bsql一对多的查询代码的查询方法是：
1、采用SQLServer。首先在SQLServer创建Student表，插入假数据，查询Student表。
2、在SQLServer创建Subject表，插入假数据，查询Subject表。注意：Student表和Subject表两表必须有id关联，否则查不了东西。
3、第一种情况：这种查询看到学生的的考了那些科目，但是分数无法看到。
4、第二种情况：这种查询可以客观地看到学生的所修的科目分数。
from 主表 d,
(select b.*
from (select id, max(时间) max_date from 从表 group by id) a,
从表 b
where a.id = b.id
and a.max_date = b.时间) c
where c.id = d.id
mybatis的动态sql编写以及一对一关系查询和一对多的查询
创建mybatis数据库,运行以下sql语句
/* SQLyog Ultimate v8.32 MySQL - 5.5.27 : Database - mybatis ********************************************************************* */ /*!40101 SET NAMES utf8 */; /*!40101 SET SQL_MODE=\'\'*/; /*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */; /*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */; /*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE=\'NO_AUTO_VALUE_ON_ZERO\' */; /*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */; /*Table structure for table `items` */ DROP TABLE IF EXISTS `items`; CREATE TABLE `items` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(32) NOT NULL COMMENT \'商品名称\', `price` float(10,1) NOT NULL COMMENT \'商品定价\', `detail` text COMMENT \'商品描述\', `pic` varchar(64) DEFAULT NULL COMMENT \'商品图片\', `createtime` datetime NOT NULL COMMENT \'生产日期\', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8; /*Data for the table `items` */ insert into `items`(`id`,`name`,`price`,`detail`,`pic`,`createtime`) values (1,\'台式机\',3333.0,\'该电脑质量非常好！！！！\',\'\',\'2015-01-01 00:00:00\'),(2,\'笔记本\',6000.0,\'笔记本性能好，质量好！！！！！\',NULL,\'2015-02-09 13:22:57\'),(3,\'背包\',200.0,\'名牌背包，容量大质量好！！！！\',NULL,\'2015-02-06 13:23:02\'); /*Table structure for table `orderdetail` */ DROP TABLE IF EXISTS `orderdetail`; CREATE TABLE `orderdetail` ( `id` int(11) NOT NULL AUTO_INCREMENT, `orders_id` int(11) NOT NULL COMMENT \'订单id\', `items_id` int(11) NOT NULL COMMENT \'商品id\', `items_num` int(11) DEFAULT NULL COMMENT \'商品购买数量\', PRIMARY KEY (`id`), KEY `FK_orderdetail_1` (`orders_id`), KEY `FK_orderdetail_2` (`items_id`), CONSTRAINT `FK_orderdetail_1` FOREIGN KEY (`orders_id`) REFERENCES `orders` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `FK_orderdetail_2` FOREIGN KEY (`items_id`) REFERENCES `items` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8; /*Data for the table `orderdetail` */ insert into `orderdetail`(`id`,`orders_id`,`items_id`,`items_num`) values (1,3,1,1),(2,3,2,3),(3,4,3,4),(4,4,2,3); /*Table structure for table `orders` */ DROP TABLE IF EXISTS `orders`; CREATE TABLE `orders` ( `id` int(11) NOT NULL AUTO_INCREMENT, `user_id` int(11) NOT NULL COMMENT \'下单用户id\', `number` varchar(32) NOT NULL COMMENT \'订单号\', `createtime` datetime NOT NULL COMMENT \'创建订单时间\', `note` varchar(100) DEFAULT NULL COMMENT \'备注\', PRIMARY KEY (`id`), KEY `FK_orders_1` (`user_id`), CONSTRAINT `FK_orders_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION ) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8; /*Data for the table `orders` */ insert into `orders`(`id`,`user_id`,`number`,`createtime`,`note`) values (3,1,\'1000010\',\'2015-02-04 13:22:35\',NULL),(4,1,\'1000011\',\'2015-02-03 13:22:41\',NULL),(5,10,\'1000012\',\'2015-02-12 16:13:23\',NULL); /*Table structure for table `user` */ DROP TABLE IF EXISTS `user`; CREATE TABLE `user` ( `id` int(11) NOT NULL AUTO_INCREMENT, `username` varchar(32) NOT NULL COMMENT \'用户名称\', `birthday` date DEFAULT NULL COMMENT \'生日\', `sex` char(1) DEFAULT NULL COMMENT \'性别\', `address` varchar(256) DEFAULT NULL COMMENT \'地址\', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=27 DEFAULT CHARSET=utf8; /*Data for the table `user` */ insert into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (1,\'王五\',NULL,\'2\',NULL),(10,\'张三\',\'2014-07-10\',\'1\',\'北京市\'),(16,\'张小明\',NULL,\'1\',\'河南郑州\'),(22,\'陈小明\',NULL,\'1\',\'河南郑州\'),(24,\'张三丰\',NULL,\'1\',\'河南郑州\'),(25,\'陈小明\',NULL,\'1\',\'河南郑州\'),(26,\'王五\',NULL,NULL,NULL); /*!40101 SET SQL_MODE=@OLD_SQL_MODE */; /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */; /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */; /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
创建工程包结构,以及导入jar包
log4j的配置文件
### direct log messages to stdout ### log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.Target=System.err log4j.appender.stdout.layout=org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n ### direct messages to file mylog.log ### log4j.appender.file=org.apache.log4j.FileAppender log4j.appender.file.File=d:/mylog.log log4j.appender.file.layout=org.apache.log4j.PatternLayout log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n ### set log levels - for more verbose logging change \'info\' to \'debug\' ### log4j.rootLogger=debug, stdout
db.properties数据库连接配置文件
jdbc.driverClassName=com.mysql.jdbc.Driver jdbc.url=jdbc:mysql://localhost:3306/mybatis jdbc.username=root jdbc.password=123
SqlMapConfig.xml全局的配置文件,mybatis必须的配置文件
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <properties resource="db.properties"> </properties> <typeAliases> <!-- 批量别名定义，扫描整个包下的类，别名为类名（大小写不敏感） --> <package name="com.baoyuan.mybatis"/> </typeAliases> <!--名称随意 --> <environments default="development"> <!--id必须和上面的一致 --> <environment id="development"> <!--固定格式JDBC --> <transactionManager type="JDBC"></transactionManager> <dataSource type="POOLED"> <property name="driver" value="${jdbc.driverClassName}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </dataSource> </environment> </environments> <mappers> <!-- 注意：此种方法要求mapper接口名称和mapper映射文件名称相同，且放在同一个目录中。 --> <package name="com.baoyuan.mybatis.mapper"/> </mappers> </configuration>
user这个pojo类
package com.baoyuan.mybatis.pojo; import java.util.Date; import java.util.List; public class User { private Integer id; private String username;// 用户姓名 private String sex;// 性别 private Date birthday;// 生日 private String address;// 地址 private List<Order> orders; public List<Order> getOrders() { return orders; } public void setOrders(List<Order> orders) { this.orders = orders; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } @Override public String toString() { return "User [id=" + id + ", username=" + username + ", sex=" + sex + ", birthday=" + birthday + ", address=" + address + ", orders=" + orders + "]"; } }
user和order一对多关联查询使用resultType方式定义的pojo类
package com.baoyuan.mybatis.pojo; import java.util.Date; public class UserOrder extends User{ private String number; private Date createtime; private String note; public String getNumber() { return number; } public void setNumber(String number) { this.number = number; } public Date getCreatetime() { return createtime; } public void setCreatetime(Date createtime) { this.createtime = createtime; } public String getNote() { return note; } public void setNote(String note) { this.note = note; } @Override public String toString() { return "UserOrder ["+super.toString()+"number=" + number + ", createtime=" + createtime + ", note=" + note + "]"; } }
user进行xml(<if><foreach><where>等)标签使用测试用到的pojo类
package com.baoyuan.mybatis.pojo; import java.util.List; public class UserWarp { private User user; private List<Integer> ids; public List<Integer> getIds() { return ids; } public void setIds(List<Integer> ids) { this.ids = ids; } public User getUser() { return user; } public void setUser(User user) { this.user = user; } @Override public String toString() { return "UserWarp [user=" + user + ", ids=" + ids + "]"; } }
user 的mapper接口
package com.baoyuan.mybatis.mapper; import java.util.List; import com.baoyuan.mybatis.pojo.User; import com.baoyuan.mybatis.pojo.UserOrder; import com.baoyuan.mybatis.pojo.UserWarp; public interface UserMapper { public User findUserById(Integer id); public List<User> findUserByusername(String username); public List<User> findUserByWhere(User user); //select * from user wehre id in (1,3,5) public List<User> findUserByIds(UserWarp userWarp); //查询所有 public List<User> findUserByAll(); //查询用户及其下的订单详情 public List<UserOrder> findUserOrdersById(Integer id); public List<User> findUserOrdersByIdToMap(Integer id); }
UserMapper.xml配置文件
<?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.baoyuan.mybatis.mapper.UserMapper"> <select id="findUserById" parameterType="int" resultType="user"> select * from user where id =#{id} </select> <select id="findUserByusername" parameterType="java.lang.String" resultType="user"> select * from user where username like \'%${value}%\' </select> <select id="findUserByWhere" parameterType="user" resultType="user"> select * from user <!-- where 自动去掉第一个and --> <where> <!--判断然后添加条件 --> <if test="id != null and id != \'\'"> and id =#{id} </if> <if test="username != null and username != \'\'"> and username like \'%${username}%\' </if> </where> </select> <!-- 使用包装类型查询用户 使用ognl从对象中取属性值，如果是包装对象可以使用【属性.XXX.XXX】来取内容的属性 --> <select id="findUserByWarp" parameterType="userWarp" resultType="user"> select * from user where username like ${user.username} </select> <!--查询Id为(1,3,5)的用户 select * from user where id in (1,2,3) --> <select id="findUserByIds" parameterType="userWarp" resultType="user"> select * from user <where> <!--如果Ids不为null,并且部位\'\' --> <if test="ids!=null"> <!-- open:表示用什么开始 close:表示用什么结束 separator:表示用什么分割 --> <foreach collection="ids" open="and id in (" close=")" separator="," item="id"> #{id} </foreach> </if> </where> </select> <select id="findUserByAll" resultType="user"> <!--include 表示运哪个sql片段 注意：如果引用其它mapper.xml的sql片段，则在引用时需要加上namespace，如下：<include refid="namespace.sql片段”/> --> <include refid="query_all" /> user </select> <!--sql片段的抽取 --> <sql id="query_all"> select * from </sql> <!--set自动去掉多余的,为null和\'\'就不进行更新 --> <update id="updateUserByWhere" parameterType="user"> UPDATE `user`
<--set会自动去掉多余的","-->
<set>
<if test="username!=null and username!=\'\'">
username = #{username},
</if>
<if test="sex!=null and sex!=\'\'">
sex = #{sex},
</if>
<if test="address!=null and address!=\'\'">
address = #{address},
</if>
</set>
WHERE
id = #{id} </update> <!--一对多关联查询 :查询用户及其下的订单详情 --> <select id="findUserOrdersById" resultType="UserOrder" parameterType="int"> SELECT u.*, o.id , o.createtime, o.note, o.number FROM `user` u LEFT JOIN `order` o ON u.id = o.user_id WHERE u.id=#{id} </select> <resultMap type="user" id="find_user_order_byid"> <!-- 用户信息映射 --> <id property="id" column="id"/> <result property="username" column="username"/> <result property="birthday" column="birthday"/> <result property="sex" column="sex"/> <result property="address" column="address"/> <!-- 一对多关联映射 property;表示属性名称 ofType:表示映射的类的全路径,这里写的是别名 --> <collection property="orders" ofType="order"> <!--用户id已经在user对象中存在，此处可以不设置--> <!-- <result property="userId" column="id"/> --> <result property="number" column="number"/> <result property="createtime" column="createtime"/> <result property="note" column="note"/> </collection> </resultMap> <!--一对多关联查询 :查询用户及其下的订单详情 ,使用resultMap --> <select id="findUserOrdersByIdToMap" resultMap="find_user_order_byid" parameterType="int"> SELECT u.*, o.id , o.createtime, o.note, o.number FROM `user` u LEFT JOIN `order` o ON u.id = o.user_id WHERE u.id=#{id} </select> </mapper>
user的测试代码
package com.baoyuan.mybatis.test; import java.io.IOException; import java.io.InputStream; import java.util.ArrayList; import java.util.List; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Before; import org.junit.Test; import com.baoyuan.mybatis.mapper.OrderMapper; import com.baoyuan.mybatis.mapper.UserMapper; import com.baoyuan.mybatis.pojo.User; import com.baoyuan.mybatis.pojo.UserOrder; import com.baoyuan.mybatis.pojo.UserWarp; public class TestUserMapper { private SqlSessionFactory sqlSessionFactory; //在运行test之前给sqlsessionfactory 赋值 @Before public void init() throws IOException{ SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder(); InputStream inputStream=Resources.getResourceAsStream("SqlMapConfig.xml"); this.sqlSessionFactory= builder.build(inputStream); } //根据Id查询用户 @Test public void findUserById(){ SqlSession sqlSession=null; try { sqlSession = sqlSessionFactory.openSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); User user = mapper.findUserById(1); System.out.println(user); } catch (Exception e) { e.printStackTrace(); }finally{ if(sqlSession!=null){ sqlSession.close(); } } } //根据用户名模糊查询 @Test public void findUserByusername(){ SqlSession sqlSession=null; try { sqlSession = sqlSessionFactory.openSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); List<User> list = mapper.findUserByusername("王"); System.out.println(list); } catch (Exception e) { e.printStackTrace(); }finally{ if(sqlSession!=null){ sqlSession.close(); } } } //根据不同条件查询 @Test public void findUserByWhere(){ SqlSession sqlSession=null; try { sqlSession = sqlSessionFactory.openSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); User user=new User(); user.setId(1); user.setUsername("狗"); List<User> list = mapper.findUserByWhere(user); System.out.println(list); } catch (Exception e) { e.printStackTrace(); }finally{ if(sqlSession!=null){ sqlSession.close(); } } } //根据一堆id查询是这些id的用户 @Test public void findUserByIds(){ SqlSession sqlSession=null; try { sqlSession = sqlSessionFactory.openSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); UserWarp userWarp=new UserWarp(); List<Integer> ids=new ArrayList<>(); ids.add(1); ids.add(3); ids.add(5); userWarp.setIds(ids); List<User> list = mapper.findUserByIds(userWarp); System.out.println(list); } catch (Exception e) { e.printStackTrace(); }finally{ if(sqlSession!=null){ sqlSession.close(); } } } //查询所有用户 @Test public void findUserByAll(){ SqlSession sqlSession=null; try { sqlSession = sqlSessionFactory.openSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); List<User> list = mapper.findUserByAll(); System.out.println(list); } catch (Exception e) { e.printStackTrace(); }finally{ if(sqlSession!=null){ sqlSession.close(); } } } //查询用户及其下的订单详情 @Test public void findUserOrdersById(){ SqlSession sqlSession=null; try { sqlSession = sqlSessionFactory.openSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); List<UserOrder> list = mapper.findUserOrdersById(1); System.out.println(list); } catch (Exception e) { e.printStackTrace(); }finally{ if(sqlSession!=sql 一对多查询