MySQL多表&JDBC

1、外键
主表：主键。从表：外键。
从表外键类型，必须与主表主键类型一致。
从表外键的值是对主表主键的引用。

注意：
从表外键不能添加主表中不存在的记录；
主表不能删除从表中已经引用的记录。

数据准备：

create table category(    cid varchar(32) primary key,    cname varchar(100));create table product(    pid varchar(32) primary key,    pname varchar(40),    price double,    category_id varchar(32));insert into category(cid,cname) values('c001','家电');insert into category(cid,cname) values('c002','服饰');insert into category(cid,cname) values('c003','化妆品');insert into product(pid,pname,price,category_id) values('p001','联想','5000','c001');insert into product(pid,pname,price,category_id) values('p002','海尔','5000','c001');insert into product(pid,pname,price,category_id) values('p003','雷神','5000','c001');insert into product(pid,pname,price,category_id) values('p004','JACK JONES','800','c002');insert into product(pid,pname,price,category_id) values('p005','真维斯','200','c002');insert into product(pid,pname,price,category_id) values('p006','花花公子','440','c002');insert into product(pid,pname,price,category_id) values('p007','劲霸','2000','c002');insert into product(pid,pname,price,category_id) values('p008','香奈儿','800','c003');insert into product(pid,pname,price,category_id) values('p009','相宜本草','200','c003');

添加约束：

alter table product add foreign key(category_id) references category(cid);

2、表和表的关系
一对多：主表和从表；
多对多：两个主表和一个从表。

//订单表create table orders(    oid varchar(32) primary key,    totalprice double);//订单项表create table orderitem(    oid varchar(50),    pid varchar(50));//联合主键alter table orderitem add primary key(oid,pid);//订单表和订单项表的主外键关系alter table orderitem add constraint orderitem_orders_fk foreign key(oid) references orders(oid);//订单表和product表的主外键关系alter table orderitem add constraint orderitem1_product_fk foreign key(pid) references product(pid);

3、查询
3.1、多表查询

内连接：

SELECT * FROM category INNER JOIN product ON cid=category_id;

或者：

SELECT * FROM category c,product p WHERE c.cid = p.category_id;

外连接：

SELECT * FROM category LEFT JOIN product ON cid=category_id;SELECT * FROM category RIGHT JOIN product ON cid=category_id;

左外连接：左表全部及两个表的交集；
内连接：查询两个表交集；
右外连接：右表全部及两个表的交集。

3.2、子查询
一条select语句结果作为另一条select语法一部分。

SELECT * FROM product WHERE category_id = (SELECT cid FROM category WHERE cname='化妆品');

4、工具类

工具类一

import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;public class JDBCUtils_V1 {    /**     * 获取连接方法     * @return     */    public static Connection getConnection() {        Connection conn = null;        try {            Class.forName("com.mysql.jdbc.Driver");            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/web", "root", "******");        } catch (Exception e) {            e.printStackTrace();        }        return conn;    }    public static void release(Connection conn, PreparedStatement pstmt, ResultSet rs) {        if (rs != null) {            try {                rs.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (pstmt != null) {            try {                pstmt.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (conn != null) {            try {                conn.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }}

工具类一的使用：

/** * 根据id查询用户信息 */@Testpublic void testFindUserById() {    Connection conn = null;    PreparedStatement pstmt = null;    ResultSet rs = null;    try {        // 1.获取连接        conn = JDBCUtils_V1.getConnection();        // 2.编写sql语句        String sql = "select * from tbl_user where uid=?";        // 3.获取执行sql语句对象        pstmt = conn.prepareStatement(sql);        // 4.设置参数        pstmt.setInt(1, 2);        // 5.执行查询操作        rs = pstmt.executeQuery();        // 6.处理结果集        while (rs.next()) {            System.out.println(rs.getString(2) + "----" + rs.getString("upassword"));        }        // 释放资源放在此处行么？【不行滴！】    } catch (SQLException e) {        e.printStackTrace();    } finally {        // 7.释放资源        JDBCUtils_V1.release(conn, pstmt, rs);    }}

工具类二
新建xx.properties文件：

driver=com.mysql.jdbc.Driverurl=jdbc:mysql://localhost:3306/web?useUnicode=true&characterEncoding=utf8username=rootpassword=****

properties文件建议放在src下，一行一组数据，格式是key=value,value不支持中文。不要加空格。

import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ResourceBundle;public class JDBCUtils_V2 {    private static String driver;    private static String url;    private static String username;    private static String password;     /**     * 静态代码块加载配置文件信息     */    static{        ResourceBundle bundle = ResourceBundle.getBundle("xx");        driver = bundle.getString("driver");        url = bundle.getString("url");        username = bundle.getString("username");        password = bundle.getString("password");    }    /**     * 获取连接方法     *      * @return     */    public static Connection getConnection() {        Connection conn = null;        try {            Class.forName(driver);            conn = DriverManager.getConnection(url, username, password);        } catch (Exception e) {            e.printStackTrace();        }        return conn;    }    public static void release(Connection conn, PreparedStatement pstmt, ResultSet rs) {        if (rs != null) {            try {                rs.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (pstmt != null) {            try {                pstmt.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (conn != null) {            try {                conn.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }}

使用:

/** * 添加用户信息方法 */@Testpublic void testAdd() {    Connection conn = null;    PreparedStatement pstmt = null;    try {        // 1.获取连接        conn = JDBCUtils_V2.getConnection();        // 2.编写sql语句        String sql = "insert into tbl_user values(null,?,?)";        // 3.获取执行sql语句对象        pstmt = conn.prepareStatement(sql);        // 4.设置参数        pstmt.setString(1, "lisi");        pstmt.setString(2, "hehe");        // 5.执行插入操作        int row = pstmt.executeUpdate();        if (row > 0) {            System.out.println("添加成功!");        } else {            System.out.println("添加失败!");        }    } catch (Exception e) {        throw new RuntimeException(e);    } finally {        // 6.释放资源        JDBCUtils_V2.release(conn, pstmt, null);    }}

工具类三
进一步对properties文件处理

import java.io.IOException;import java.io.InputStream;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.Properties;import java.util.ResourceBundle;public class JDBCUtils_V3 {    private static String driver;    private static String url;    private static String username;    private static String password;    /**     * 静态代码块加载配置文件信息     */    static {        try {            // 1.通过当前类获取类加载器            ClassLoader classLoader = JDBCUtils_V3.class.getClassLoader();            // 2.通过类加载器的方法获得一个输入流            InputStream is = classLoader.getResourceAsStream("xx.properties");            // 3.创建一个properties对象            Properties props = new Properties();            // 4.加载输入流            props.load(is);            // 5.获取相关参数的值            driver = props.getProperty("driver");            url = props.getProperty("url");            username = props.getProperty("username");            password = props.getProperty("password");        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * 获取连接方法     *      * @return     */    public static Connection getConnection() {        Connection conn = null;        try {            Class.forName(driver);            conn = DriverManager.getConnection(url, username, password);        } catch (Exception e) {            e.printStackTrace();        }        return conn;    }    public static void release(Connection conn, PreparedStatement pstmt, ResultSet rs) {        if (rs != null) {            try {                rs.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (pstmt != null) {            try {                pstmt.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (conn != null) {            try {                conn.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }}

使用

/** * 根据id更新用户信息方法 */@Testpublic void testUpdateById() {    Connection conn = null;    PreparedStatement pstmt = null;    try {        // 1.获取连接        conn = JDBCUtils_V3.getConnection();        // 2.编写sql语句        String sql = "update tbl_user set upassword=? where uid=?";        // 3.获取执行sql语句对象        pstmt = conn.prepareStatement(sql);        // 4.设置参数        pstmt.setString(1, "999");        pstmt.setInt(2, 3);        // 5.执行更新操作        int row = pstmt.executeUpdate();        if (row > 0) {            System.out.println("更新成功!");        } else {            System.out.println("更新失败!");        }    } catch (Exception e) {        throw new RuntimeException(e);    } finally {        // 6.释放资源        JDBCUtils_V3.release(conn, pstmt, null);    }}/** * 根据id删除信息方法 */@Testpublic void testDeleteById() {    Connection conn = null;    PreparedStatement pstmt = null;    try {        // 1.获取连接        conn = JDBCUtils_V3.getConnection();        // 2.编写sql语句        String sql = "delete from tbl_user where uid=?";        // 3.获取执行sql语句对象        pstmt = conn.prepareStatement(sql);        // 4.设置参数        pstmt.setInt(1, 4);        // 5.执行删除操作        int row = pstmt.executeUpdate();        if (row > 0) {            System.out.println("删除成功!");        } else {            System.out.println("删除失败!");        }    } catch (Exception e) {        throw new RuntimeException(e);    } finally {        // 6.释放资源        JDBCUtils_V3.release(conn, pstmt, null);    }}