Java(13)SQL

Java(13)SQL

1. SQL language foundation

1. 1. Inquiry

1. Basic format

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. Query a field

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

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3. Check all

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

4. Joint query

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

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5. Other functions

(1) Sort

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

(2) Total number of records

select count * as totalcount from table

(3) Sum

select sum(field1) as sumvalue from table

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(4) Average

select avg(field1) as avgvalue from table

(5) Maximum

select max(field1) as maxvalue from table

(6) Minimum

selecy min(field) as minvalue from table

1. 2. Insert

1. Basic format

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

2. Insert record (complete)

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

3. Insert a field

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

1. 3. Modification

1. Basic format

UPDATE 数据表名 SET 赋值列表 [WHERE 逻辑表达式]

2. Modify a record

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

1. 4. Delete

1. Basic format

DELETE FROM 数据表名 [WHERE 逻辑表达式]

2. Delete based on ID

DELETE FROM contactTable WHERE contactID = '1008'

2. Use of java program

2. 1. Common Framework

1. DriverManager

getConnection() establish connection

2. Connection

Establish a connection to the database

3. Statement

Execute database statement

4. ResultSet

Object class for storing results

2. 2. Steps

1. Load the driver
2. Create database connection
3. Create Statement instance
4. Execute query
5. Processing query result set
6. Close database connection

2. 3. Realization

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();
			}
		}
		
	}
}