数据库SQL的练习
2016-11-07 18:17
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已知考生表tdb_ks包含：考号?,姓名,成绩字段
表结构：
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| number | int(11) | NO | | NULL | |
| name | varchar(50) | NO | | NULL | |
| grade | int(11) | NO | | NULL | |
+--------+-------------+------+-----+---------+----------------+
表记录:
+----+--------+------+-------+
| id | number | name | grade |
+----+--------+------+-------+
| 1 | 1001 | 小明 | 89 |
| 2 | 1002 | 小丽 | 79 |
| 3 | 1003 | 张三 | 85 |
| 4 | 1004 | 李四 | 99 |
+----+--------+------+-------+
程序实现如下要求:
1>通过可视化工具创建数据库和表,要求定义id为主键并且自动增长.
2>定义方法addStudent(Student student)
功能:向考生表添加记录
3>方法printMessageAllStudent()
功能:打印所有考生信息
4>方法 updateStudentByName(Student student,String name)
功能:根据姓名更改考生信息
5>方法 deleteStudentById(int number)
功能:根据考号删除考生
6>方法 int getSum()
功能:查询所有学生总成绩
7>方法 List<Student> getAllStudent()
功能：查询高于平均分的所有学生
先建立学生类对象
public class Student {
private int number;
private String name;
private int grade;
public Student(int number, String name, int grade) {
this.number = number;
this.name = name;
this.grade = grade;
}
public int getNumber() {
return number;
}
public void setNumber(int number) {
this.number = number;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getGrade() {
return grade;
}
public void setGrade(int grade) {
this.grade = grade;
}
@Override
public String toString() {
return "Student [number=" + number + ", name=" + name + ", grade=" + grade + "]";
}
}
在创建连接 （用封装方法）
public class CouneDB {
private static final String url =（统一资源定位符）
private static final String user = "root";（连接端口）
private static final String password = "154331";（密码）
public void CouneDB() {
try {
Class.forName("com.mysql.jpbc.Driver"); （加载相对应的mysql驱动）
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public Connection getConnection() {
Connection connect = null;
try {
connect = DriverManager.getConnection(url, user, password);
} catch (SQLException e) {
e.printStackTrace();
}
return connect;
}
public void closeConnection(Connection connect) {
try {
if (connect != null)
connect.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
3.内容
public class StudentDB extends CouneDB {
private static StudentDB DB = null;
public static StudentDB getInstance() {
if (DB == null) {
DB = new StudentDB();
}
return DB;
}
private StudentDB() {
}
public void addStudent(Student student) {
String sql = "insert into tdb_ks (number,name,grade) values(?,?,?)";
Connection connect = null;
PreparedStatement ps = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
ps.setInt(1, student.getNumber());
ps.setString(2, student.getName());
ps.setInt(3, student.getGrade());
ps.execute();
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
closeConnection(connect);
}
}
public ArrayList<Student> printMessageAllStudent() {
String sql = "select * from tdb_ks";
Connection connect = null;
PreparedStatement ps = null;
ResultSet rs = null;
ArrayList<Student> studentList = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
rs = ps.executeQuery();
studentList = new ArrayList<>();
while (rs.next()) {
int number = rs.getInt("number");
String name = rs.getString("name");
int grade = rs.getInt("grade");
Student student = new Student(number, name, grade);
studentList.add(student);
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
}
return studentList;
}
public void updateStudentByName(Student student, String name) {
String sql = "update tdb_ks set grade = ? where name = ?";
Connection connect = null;
PreparedStatement ps = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
ps.setInt(1, student.getGrade());
ps.setString(2, name);
ps.execute(
97f1
);
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
}
}
public void deleteStudentById(int number) {
String sql = "delete from tdb_ks where number=?";
Connection connect = null;
PreparedStatement ps = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
ps.setInt(1, number);
ps.execute();
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
closeConnection(connect);
}
}
public int getSum() {
String sql = "select sum(grade) from tdb_ks;";
Connection connect = null;
PreparedStatement ps = null;
ResultSet rs = null;
int sum=-1;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
rs = ps.executeQuery();
System.out.println("姓名" + "\t" + "学号" + "\t" + "成绩");
if(rs.next()){
sum = rs.getInt(1);
}
} catch (SQLException e) {
e.printStackTrace();
}finally {
try {
if(ps!= null)
ps.close();
} catch (SQLException e) {
e.printStackTrace();
}
closeConnection(connect);
}
return sum;
}
public void printAllStudent(ArrayList<Student>studentList){
System.err.println("学号" + "\t" + "姓名" + "\t" + "成绩" );
for (Student student : studentList) {
System.out.println(student.getNumber()+ "\t" + student.getName()
+ "\t" + student.getGrade());
}
}
public List<Student> getAllStudent(){
String sql = "SELECT * FROM tdb_ks WHERE grade > (SELECT AVG(grade) FROM tdb_ks)";
Connection connect =null;
PreparedStatement ps = null;
ResultSet rs = null;
List<Student> list = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
rs = ps.executeQuery();
list = new ArrayList<>();
while (rs.next()) {
int number = rs.getInt("number");
String name = rs.getString("name");
int grade = rs.getInt("grade");
Student student = new Student(number, name, grade);
list.add(student);
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
}
return list;
}
public static void main(String[] args) {
StudentDB db = StudentDB.getInstance();
添加数据
db.addStudent(new Student(1001, "小明", 89));
db.addStudent(new Student(1002, "小丽", 79));
db.addStudent(new Student(1003, "张三", 85));
db.addStudent(new Student(1004, "李四", 89));
显示数据
db.printAllStudent(db.printMessageAllStudent())；
删除
db.deleteStudentById(1001);
总和
System.out.println(db.getSum());
修改
db.updateStudentByName(new Student(1004, "李四", 99), "李四");
比平均值大
ArrayList<Student> list = (ArrayList<Student>) db.getAllStudent();
for (Student student : list) {
System.out.println(student);
}
}
}
表结构：
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| number | int(11) | NO | | NULL | |
| name | varchar(50) | NO | | NULL | |
| grade | int(11) | NO | | NULL | |
+--------+-------------+------+-----+---------+----------------+
表记录:
+----+--------+------+-------+
| id | number | name | grade |
+----+--------+------+-------+
| 1 | 1001 | 小明 | 89 |
| 2 | 1002 | 小丽 | 79 |
| 3 | 1003 | 张三 | 85 |
| 4 | 1004 | 李四 | 99 |
+----+--------+------+-------+
程序实现如下要求:
1>通过可视化工具创建数据库和表,要求定义id为主键并且自动增长.
2>定义方法addStudent(Student student)
功能:向考生表添加记录
3>方法printMessageAllStudent()
功能:打印所有考生信息
4>方法 updateStudentByName(Student student,String name)
功能:根据姓名更改考生信息
5>方法 deleteStudentById(int number)
功能:根据考号删除考生
6>方法 int getSum()
功能:查询所有学生总成绩
7>方法 List<Student> getAllStudent()
功能：查询高于平均分的所有学生
先建立学生类对象
public class Student {
private int number;
private String name;
private int grade;
public Student(int number, String name, int grade) {
this.number = number;
this.name = name;
this.grade = grade;
}
public int getNumber() {
return number;
}
public void setNumber(int number) {
this.number = number;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getGrade() {
return grade;
}
public void setGrade(int grade) {
this.grade = grade;
}
@Override
public String toString() {
return "Student [number=" + number + ", name=" + name + ", grade=" + grade + "]";
}
}
在创建连接 （用封装方法）
public class CouneDB {
private static final String url =（统一资源定位符）
private static final String user = "root";（连接端口）
private static final String password = "154331";（密码）
public void CouneDB() {
try {
Class.forName("com.mysql.jpbc.Driver"); （加载相对应的mysql驱动）
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public Connection getConnection() {
Connection connect = null;
try {
connect = DriverManager.getConnection(url, user, password);
} catch (SQLException e) {
e.printStackTrace();
}
return connect;
}
public void closeConnection(Connection connect) {
try {
if (connect != null)
connect.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
3.内容
public class StudentDB extends CouneDB {
private static StudentDB DB = null;
public static StudentDB getInstance() {
if (DB == null) {
DB = new StudentDB();
}
return DB;
}
private StudentDB() {
}
public void addStudent(Student student) {
String sql = "insert into tdb_ks (number,name,grade) values(?,?,?)";
Connection connect = null;
PreparedStatement ps = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
ps.setInt(1, student.getNumber());
ps.setString(2, student.getName());
ps.setInt(3, student.getGrade());
ps.execute();
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
closeConnection(connect);
}
}
public ArrayList<Student> printMessageAllStudent() {
String sql = "select * from tdb_ks";
Connection connect = null;
PreparedStatement ps = null;
ResultSet rs = null;
ArrayList<Student> studentList = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
rs = ps.executeQuery();
studentList = new ArrayList<>();
while (rs.next()) {
int number = rs.getInt("number");
String name = rs.getString("name");
int grade = rs.getInt("grade");
Student student = new Student(number, name, grade);
studentList.add(student);
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
}
return studentList;
}
public void updateStudentByName(Student student, String name) {
String sql = "update tdb_ks set grade = ? where name = ?";
Connection connect = null;
PreparedStatement ps = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
ps.setInt(1, student.getGrade());
ps.setString(2, name);
ps.execute(
97f1
);
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
}
}
public void deleteStudentById(int number) {
String sql = "delete from tdb_ks where number=?";
Connection connect = null;
PreparedStatement ps = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
ps.setInt(1, number);
ps.execute();
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
closeConnection(connect);
}
}
public int getSum() {
String sql = "select sum(grade) from tdb_ks;";
Connection connect = null;
PreparedStatement ps = null;
ResultSet rs = null;
int sum=-1;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
rs = ps.executeQuery();
System.out.println("姓名" + "\t" + "学号" + "\t" + "成绩");
if(rs.next()){
sum = rs.getInt(1);
}
} catch (SQLException e) {
e.printStackTrace();
}finally {
try {
if(ps!= null)
ps.close();
} catch (SQLException e) {
e.printStackTrace();
}
closeConnection(connect);
}
return sum;
}
public void printAllStudent(ArrayList<Student>studentList){
System.err.println("学号" + "\t" + "姓名" + "\t" + "成绩" );
for (Student student : studentList) {
System.out.println(student.getNumber()+ "\t" + student.getName()
+ "\t" + student.getGrade());
}
}
public List<Student> getAllStudent(){
String sql = "SELECT * FROM tdb_ks WHERE grade > (SELECT AVG(grade) FROM tdb_ks)";
Connection connect =null;
PreparedStatement ps = null;
ResultSet rs = null;
List<Student> list = null;
try {
connect = getConnection();
ps = connect.prepareStatement(sql);
rs = ps.executeQuery();
list = new ArrayList<>();
while (rs.next()) {
int number = rs.getInt("number");
String name = rs.getString("name");
int grade = rs.getInt("grade");
Student student = new Student(number, name, grade);
list.add(student);
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
}
}
}
return list;
}
public static void main(String[] args) {
StudentDB db = StudentDB.getInstance();
添加数据
db.addStudent(new Student(1001, "小明", 89));
db.addStudent(new Student(1002, "小丽", 79));
db.addStudent(new Student(1003, "张三", 85));
db.addStudent(new Student(1004, "李四", 89));
显示数据
db.printAllStudent(db.printMessageAllStudent())；
删除
db.deleteStudentById(1001);
总和
System.out.println(db.getSum());
修改
db.updateStudentByName(new Student(1004, "李四", 99), "李四");
比平均值大
ArrayList<Student> list = (ArrayList<Student>) db.getAllStudent();
for (Student student : list) {
System.out.println(student);
}
}
}
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