关于数据库使用基本操作

连接SQL的语句：
    Connection con=null;
    Statement stmt=null;
    PreparedStatement ps=null;
    ResultSet rs=null;
    String sql=null;
    public dbconn(){
    
    }

         try{
     Class.forName("com.microsoft.jdbc.sqlserve.SQLServerDriver").newInstance();
     String url="jdbc:microsoft:sqlserver://localhost:8080;DatabaseName=data";
                   //这是SQL server语句
               Class.forName("org.git.mm.mysql.Driver").newInstance();
     DriverManager.getConnection("jdbc:mysql://localhost:8080;DatabaseName=data","admin","123");
                      //这是mysql语句
                 Class.forName("oracle.jdbc.driver.OracleDriver").newInstance();
                 DriverManager.getConnection("jdbc:mysql://localhost/studentData?user=username&";...characterEncoding=8859-1");
     String username="admin";
     String password="123";
     con=DriverManager.getConnection(url,username,password);
     }catch(Exception e){
     System.out.println("连接数据库失败。");
     e.printStackTrace();
     }

    
sql中数据处理语句：
int num=0;
     try{
     stmt=con.createStatement();
    
     stmt.executeUpdate(sql);
     }catch(Exception e){
     e.printStackTrace();
     }
return num;

sql中统计语句：
int num=0;
     try{
     stmt=con.createStatement();
     rs=stmt.executeQuery(sql);
     while(rs.next()){
     num=rs.getInt(1);
     }
     }
     catch(Exception e){
     e.printStackTrace();
     }
     return num;
sql中关闭sql：
try{
     if(rs!=null){
     rs.close();
     rs=null;