Summary of simple methods for C# program to connect to database and read fields in database

string connStr = @"Data Source=D:\; Provider=.4.0;"; //Database connection stringOleDbConnection conn = new OleDbConnection(connStr); 

//The database and client are on the same machineusing ; 
string connStr = "data source=orcl;user=user;password=pwd;"; 
OracleConnection conn = new OracleConnection(connStr); 
//The client and the database are not on the same machine, you can use the following connection methodusing ; 
//HOST is the Oracle database server address, PORT is the Oracle database port, SERVICE_NAME is the database namestring connStr = "Provider=.1;Data Source=(DESCRIPTION =(ADDRESS_LIST =(ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521)))(CONNECT_DATA =(SERVICE_NAME = orcl)));User ID=message;Password=message;"; 
OleDbConnection conn = new OleDbConnection(connStr); 

using ; 
string connStr = "data source=127.0.0.1;initial catalog=database;user id=sa;pwd=sa"; 
SqlConnection conn = new SqlConnection(connStr); 

using System; 
using ; 
using ; 
using ; 
using ; 
 
namespace Login 
{ 
 class Program 
 { 
  static void Main(string[] args) 
  { 
   // Create a new database connection   using(SqlConnection conn = new SqlConnection(GetConnectString())) 
   { 
    ();//Open the database    //("The database is opened successfully!");    //Create a database command    SqlCommand cmd = (); 
    //Create a query statement     = "SELECT * FROM userinfo"; 
    //Read the data stream from the database and store it into the reader    SqlDataReader reader = ();     
     
    //Read the next row of data from the reader. If there is no data, () returns flase    while (()) 
    { 
     //("id") is the index of the column where the ID is located,     //reader.GetInt32(int n) This returns the data in column n in the format of Int32     //(int n) This is to return the data of column n in string format     int id = reader.GetInt32(("id")); 
     string name = (("name")); 
     string pwd = (("password")); 
     int age = reader.GetInt32(("age")); 
     string sex = (("sex")); 
     string phone = (("phone")); 
     string address = (("Address")); 
 
     //Format output data     ("ID:{0},Name:{1},PWD:{2},Age:{3},Sex:{4},Phone{5},Address:{6}\n", id, name, pwd, age, sex, phone, address); 
    } 
   } 
   (); 
  } 
  //Get a database connection string  static string GetConnectString() 
  { 
   return "Data Source=(local);Initial Catalog=db1;Integrated Security=SSPI;"; 
  } 
 } 
} 

DataTable dt;        //Suppose the field is name, dt has saved the data[0]["name"] == ; //Judge whether the name field of the first line of data is empty

DataTable dt;    //Suppose the field is name, dt has saved the data[0].IsNull("name"); //Judge whether the name field of the first line of data is empty

DataTable dt;       //Suppose the field is name, dt has saved the data[0]["name"].ToString() == ""; //Judge whether the name field of the first line of data is empty