C # program to connect the database and read the fields in the database simple method Summary _c# tutorial

Connect to an Access database

string connstr = @ "Data Source=d:\database.mdb; provider=microsoft.jet.oledb.4.0; "; Database connection string 
OleDbConnection conn = new OleDbConnection (CONNSTR); 

Connecting Oracle Databases

The database and the client are using System.Data.OracleClient on the same machine 
; 
String connstr = "Data source=orcl;user=user;password=pwd;"; 
OracleConnection conn = new OracleConnection (CONNSTR); 
The client and database are not on the same machine, you can use System.Data.OleDb using the following connection method 
; 
Host is the Oracle database server address and port is the Oracle database port, service_name is the database name 
string connstr = "Provider=oraoledb.oracle.1;data Source= (DESCRIPTION = (Address_list = (address = (PROTOCOL = TCP) (HOST = 127.0.0.1) (PORT = 1521)) (Connect_data = (service_n AME = ORCL))); User Id=message; Password=message; "; 
OleDbConnection conn = new OleDbConnection (CONNSTR); 

Connecting to the SQL Server database

Using System.Data.SqlClient; 
String connstr = "Data source=127.0.0.1;initial catalog=database;user Id=sa;pwd=sa"; 
SqlConnection conn = new SqlConnection (CONNSTR); 

Connect the database and read the data from the database and output it!

Using System; 
Using System.Collections.Generic; 
Using System.Linq; 
Using System.Text; 
 
Using System.Data.SqlClient; Namespace Login {class Program {static void Main (string[] args) {//Create a new database connection using (SqlConnection con n = new SqlConnection (Getconnectstring ())) {Conn. 
    Open ()//Opens database//console.writeline ("Database open successfully!"); Create DATABASE command SqlCommand CMD = conn. 
    CreateCommand (); 
    Create a query statement cmd.commandtext = "SELECT * from UserInfo"; Read the data stream from the database into reader sqldatareader reader = cmd.     
     
    ExecuteReader (); Read the next line of data from reader, if there is no data, reader. Read () returns flase while reader. Read ()) {//reader. GetOrdinal ("id") is the index,//reader, of the column that gets the ID. GetInt32 (int n) This is to return the nth column of data in INT32 format to//reader. GetString (int n) This is to return the nth column of data to the int id = Reader in string format. GetInt32 (reader. 
     GetOrdinal ("id")); String name = Reader. GetString (reader. 
     GetOrdinal ("name")); string pwd = reader. GetString (reader. 
     GetOrdinal ("password")); Int Age = Reader. GetInt32 (reader. 
     GetOrdinal ("Age")); string sex = reader. GetString (reader. 
     GetOrdinal ("Sex")); string phone = reader. GetString (reader. 
     GetOrdinal ("Phone")); string address = reader. GetString (reader. 
 
     GetOrdinal ("Address")); Format output Data Console.Write ("id:{0},name:{1},pwd:{2},age:{3},sex:{4},phone{5},address:{6}\n", ID, Name, PWD, age, Sex, ph 
    one, address); 
  } console.readkey (); ///Get a database connection string, static string Getconnectstring () {return ' Data source= (local); Initial catalog=db1;integrate 

 D Security=sspi; ";}}}

determine if the value of the field fetched in the database is null (NULL)
the last time you manipulate a database, you need to determine whether the returned field value is empty and search for three methods on Google.

1 through System.DBNull judgment, most of the online use this method.

DataTable DT;        Assuming the field name, DT has saved the data 
dt.rows[0]["name" = = System.DBNull.Value;//To determine whether the first row of data is empty 

2 Judging by IsNull

DataTable DT;    Assuming the field name, DT has saved the data 
dt.rows[0]. IsNull ("name"); Determine if the name field of the first row of data is empty 

3 Judging by ToString (), I have not tried this method.

DataTable DT;       Assuming the field name, DT has saved the data 
dt.rows[0]["name". ToString () = = ""; Determine if the name field of the first row of data is empty