Java(13)SQL

Java(13)SQL

一. SQL语言基础

1. 1. 查询

1. 基本格式

SELECT 字段名列表 FROM 数据表名 [WHERE逻辑表达式] [ORDER BY 字段名列表]

2. 查询某字段

SELECT contactName,isFreqContact FROM contactTable WHERE contactID = '10001'

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3. 查询所有

SELECT * FROM contactTable WHERE contactName = '张三' or contactName = '李四' ORDER BY contactName DEBC
//DEBC 表示按照contactName降序

4. 联合查询

SELECT contactName,phoneNum
FROM contactTable,phoneTable
WHERE contactTable.contactID = phoneTable.contactID
and contactID = '10001'

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5. 其他函数

(1)排序

select * from table order by field1,field2 [desc]

(2)records总数

select count * as totalcount from table

(3)求和

select sum(field1) as sumvalue from table

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(4)平均

select avg(field1) as avgvalue from table

(5)最大

select max(field1) as maxvalue from table

(6)最小

selecy min(field) as minvalue from table

1. 2. 插入

1. 基本格式

INSERT INTO table [字段名列表] VALUES (字段名列表)

2. 插入记录(完整的)

INSERT INTO contactTable VALUES ('10001','王五',true)

3. 插入某字段

INSERT INTO contactTable (contactID,contactName) VALUES ('1009','赵六')

1. 3. 修改

1. 基本格式

UPDATE 数据表名 SET 赋值列表 [WHERE 逻辑表达式]

2. 修改某记录

UPDATE contactTable SET contactName = '李平',isFreqContact = true WHERE contactID = '1008'

1. 4. 删除

1. 基本格式

DELETE FROM 数据表名 [WHERE 逻辑表达式]

2. 根据ID删除

DELETE FROM contactTable WHERE contactID = '1008'

二. java程序使用

2. 1. 常见框架

1. DriverManager

getConnection() 建立连接

2. Connection

建立与数据库的连接

3. Statement

执行数据库语句

4. ResultSet

存储结果的对象类

2. 2. 步骤

1. 加载驱动
2. 创建数据库连接
3. 创建Statement实例
4. 执行查询
5. 处理查询结果集
6. 关闭数据库连接

2. 3. 实现

import java.sql.*;
public class Main {
    
    
	public static void main(String[] args) {
    
    
		//声明变量
		String url;
		Connection connection = null;
		Statement statement = null;
		String contactID;
		String contactName;
		
		//生成查询语句
		String sqlSelect = "select contactID.contactName from contactTable";
		
		//连接数据库
		try {
    
    
			//1.加载驱动
			Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
			
			//2.连接数据库
			url = "jdbc:odbc:mydataSource";
			//创建连接
			//后面是账号和密码
			connection = DriverManager.getConnection(url,"","");
			//3.创建一个Statement
			statement = connection.createStatement();
			//4，执行SQL 语句
			ResultSet result = statement.executeQuery(sqlSelect);
			
			//5.从结果龚读取数据
			while(result.next()) {
    
    
				contactID = result.getString("contactID");
				contactName = result.getString("contactName");
				System.out.println(contactID + "," + contactName);
			}
			result.close();
		} catch (SQLException e) {
    
    
			// TODO: handle exception
			System.out.println(e);
		}catch (ClassNotFoundException e) {
    
    
			// TODO: handle exception
			e.printStackTrace();
		}
		finally {
    
    
			try {
    
    
				if(statement != null) {
    
    
					statement.close();
				}
				if(connection != null) {
    
    
					connection.close();
				}
			} catch (Exception e) {
    
    
				System.out.println(e.getMessage());
				e.printStackTrace();
			}
		}
		
	}
}