mysql（二）

程序连接Mysql

1.Java代码示例JDBC客户端应用 -> java.sql.或javax.sql. -> 驱动程序 -> SQLserver/Oracle/MySQL结构：DriverManager -> Driver(是驱动程序对象的接口，指向具体数据库驱动程序对象)=DriverManager.getDriver(String URL) -> Connectinon(是连接对象接口，指向具体数据库连接对象)=DriverManager.getConnection(String URL) -> Statement(执行静态SQL语句接口)=Connection.CreateStatement() -> ResultSet(是指向结果集对象的接口)=Statement.excuteXXX()

import com.mysql.jdbc.Connection;

import java.sql.*;

import javax.swing.text.DefaultEditorKit.InsertBreakAction;

public class Conntect {

public static Connection getConnection()throws SQLException,java.lang.ClassNotFoundException
{
Class.forName("com.mysql.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/testdao";
String username= "root";
String password = "root";
Connection conn = (Connection) DriverManager.getConnection(url,username,password);
return conn;
}
public static void main(String args[]) throws SQLException
{

Connection con = null;
try
{
con = getConnection();
Statement sql_statement = con.createStatement();
sql_statement.executeUpdate("drop table if exists test;");
sql_statement.executeUpdate("create table test(user varchar(20) not null ,"
+ "leixing varchar(20) "
+ "not null,score varchar(20) not null,"
+ "primary key(user,leixing));");
String[] a= new String[]{"li","age", "18","li", "dep", "2","li","sex","male","sun","age","44","sun","sex","female","sun","dep","3","wang","age","20","wang","dep","3","wang","sex","male"};
//          System.out.println(a.length);
for(int i=0;i<a.length;i+=3)
{

//              System.out.println(i);
String sql = "insert into test values('"+a[i]+"','"+a[i+1]+"','"+a[i+2]+"');";
//              System.out.println(sql);
sql_statement.executeUpdate(sql);
}

sql_statement.execute("insert into test values('zxc','age','22');");

sql_statement.execute("update test set score='77' where user='zxc' and leixing='age';");

int num = sql_statement.executeUpdate("delete from test where user='zxc';");
System.out.println(num);

String query = "select * from test;";
ResultSet result = sql_statement.executeQuery(query);
while (result.next())
{
String cname = result.getString("user");
String cource = result.getString("leixing");
String score = result.getString("score");
System.out.println("姓名:"+cname+" 类型:"+cource+" 分数:"+score);
}
result.close();
sql_statement.close();

String sql1 = "insert into test value(?,?,?)";
PreparedStatement prsa = con.prepareStatement(sql1);
prsa.setString(1, "zxc");
prsa.setString(2, "age");
prsa.setString(3, "55");
num= prsa.executeUpdate();
System.out.println(num+"rows has insert");

String sql = "update test set score=? where user=? and leixing=?";
prsa = con.prepareStatement(sql);

prsa.setString(1, "23");

prsa.setString(2, "zxc");
prsa.setString(3, "age");

num= prsa.executeUpdate();
System.out.println(num+"rows has changed");

prsa.close();

query = "select * from test;";
PreparedStatement ps = (PreparedStatement) con.prepareStatement(query,ResultSet.TYPE_FORWARD_ONLY,ResultSet.CONCUR_READ_ONLY);
ps.setFetchSize(Integer.MIN_VALUE);
result =  ps.executeQuery();
while (result.next())
{
String cname = result.getString("user");
String cource = result.getString("leixing");
String score = result.getString("score");
System.out.println("姓名:"+cname+" 类型:"+cource+" 分数:"+score);
}

result.close();
ps.close();
con.close();
}
catch(java.lang.ClassNotFoundException e){
System.err.print("ClassNotFoundException");
}
catch(SQLException e)
{
System.err.print("SQL exception"+e.getMessage());
}

}
}

Statement与PreparedStatement的区别

connection, Statement与ResultSet关闭的意义jdbc连接参数的使用ResultSet游标的使用(setFetchSize)Statement与PreparedStatement的区别

PreparedStatement在数据库端预编译，效率高，可以防止SQL注入。

对数据库执行一次性存取的时候，用Statement对象进行处理。线上业务推荐使用PreparedStatement.connection, Statement与ResultSet关闭的意义MySQL数据库端为connection与ResultSet维护内存状态，一直不关闭会占用服务端资源。MySQL最大连接数受max_connections限制，不能无限创建连接，所以用完要及时关闭。JDBC connection关闭后ResultSet, Statement会自动关闭。但是如果使用连接池将不会关闭，因此推荐主动关闭。

ResultSet游标的使用

默认的ResultSet对象不可更新，仅有一个向前移动的指针。因此，只能迭代它一次，并且只能按从第一行到最后一行的顺序进行。可以生成可滚动和/或可更新的ResultSet对象。setFetchSize()是设置ResultSet每次向数据库取的行数，防止数据返回量过大将内存爆掉。

#####2.Python代码示例
* Python操作mysql数据库需要MySQL-python驱动
如果电脑有pip或者easyinstall可以直接安装

pip install MySQL-pythoneasy_install MySQL-python

#coding:utf-8import MySQLdbconn = MySQLdb.connect(host=”localhost”,port=3308,user=”root”,passwd=”root”)#建立与数据库的连接curs= conn.cursor()#获取游标conn.select_db(‘testdao’)#选择数据库testdaocurs.execute(“update test set score=’56’ where user=’zxc’ and leixing=’age’”)print curs.fetchone()#获取一条记录,以一个元组返回values = [(‘zxc’,’sex’,’male’),(‘zxc’,’dep’,’4’)]curs.executemany(“insert into test values(%s,%s,%s)” ,values)conn.commit()#执行插入多条数据要用exectemany,并提交curs.execute(“select * from test”)result = curs.fetchall()for item in result:print “姓名:”+item[0]+”类型:”+item[1]+”分数”+item[2]#获取所有的记录,以一个元组返回curs.close()conn.close()#关闭连接

cursor用来执行命令的方法：callproc(self,procname,args)用来执行存储过程,接收的参数为存储过程名和参数列表,返回值为受影响的行数execute(self, query, args)执行单条sql语句,接收的参数为sql语句本身和使用的参数列表,返回值为受影响的行数executemany(self, query, args)执行单挑sql语句,但是重复执行参数列表里的参数,返回值为受影响的行数nextset(self)移动到下一个结果集cursor用来接收返回值的方法：fetchall(self)接收全部的返回结果行fetchmany(self, size=None)接收size条返回结果行.如果size的值大于返回的结果行的数量,则会返回cursor.arraysize条数据fetchone(self)返回一条结果行scroll(self, value, mode=’relative’)移动指针到某一行，如果mode=’relative’,则表示从当前所在行移动value条,如果 mode=’absolute’,则表示从结果集的第一行移动value条。（ 于2016年6月21日，http://blog.csdn.net/bzd_111）