C # Connect database-Once, delete, change, check

Connecting to a database

        Static voidMain (string[] args) {            //SqlConnection conn = new SqlConnection ();//instantiation of//Conn. ConnectionString = "server=.; Database=mydb;uid=sa;pwd=123 ";//The initialization-----can be executed with one of the following statementsSqlConnection conn =NewSqlConnection ("server=.; Database=mydb;uid=sa;pwd=123"); Console.WriteLine (Conn.            State); Conn. Open ();//Open a database connectionConsole.WriteLine (Conn.            State); Conn. Close ();//To close a database connectionConsole.WriteLine (Conn.                   State); }

Connect to a database and insert data

        Static voidMain (string[] args) {SqlConnection conn=NewSqlConnection ("server=.; Database=mydb;uid=sa;pwd=123"); Conn.            Open (); SqlCommand cmd=NewSqlCommand (); Cmd. Connection= conn;//Initialize, connect to database via Conn data ObjectCmd.commandtext ="INSERT into info values (' p005 ', ' student ', ' 0 ', ' n001 ', ' 1990-02-1 ')";//" " in the SQL statementcmd.            ExecuteNonQuery (); Conn.            Close (); Console.WriteLine ("OK"); }

Connect to the database and modify the data

         Public Static voidMain (string[] args) {SqlConnection conn=NewSqlConnection ("server=.; Database=mydb;uid=sa;pwd=123"); Conn.            Open (); SqlCommand cmd=NewSqlCommand (); Cmd. Connection=Conn; Cmd.commandtext="Update info set name= ' learner ' where code= ' p005 '"; Cmd.            ExecuteNonQuery (); Conn.        Close (); }

Connect to the database and delete the data

  public  static  void  Main (string  [] args) {Sq Lconnection conn  = "  server=.;                                           database=mydb;uid=sa;pwd=123   ); Conn.                        Open (); SqlCommand cmd  = Conn.            CreateCommand (); Cmd.commandtext  =  delete from info where code            = ' p005 '   " ; Cmd.            ExecuteNonQuery (); Conn.                   Close (); }

Connecting database query data

        Static voidMain (string[] args) {SqlConnection conn=NewSqlConnection ("server=.; Database=mydb;uid=sa;pwd=123"); Conn.            Open (); SqlCommand cmd=Conn.            CreateCommand (); Cmd.commandtext="SELECT * FROM Info"; SqlDataReader R= cmd. ExecuteReader ();//Query statement returns SqlDataReader class with ExecuteReader             while(R.read ()) {Console.WriteLine (r[0]. ToString () +r[1]. ToString () +r[2].            ToString ()); } conn.        Close (); }

Case: User Login implementation

         Public Static voidMain (string[] arges) {Console.Write ("User name:"); stringUID =Console.ReadLine (); Console.Write ("Password:"); stringPWD =Console.ReadLine (); SqlConnection Conn=NewSqlConnection ("server=.; Database=mydb;uid=sa;pwd=123"); Conn.            Open (); SqlCommand cmd=Conn.            CreateCommand (); Cmd.commandtext="SELECT * FROM login where username= '"+uid+"' and password= '"+pwd+"'"; SqlDataReader R=cmd.            ExecuteReader (); if(R.hasrows = =false) {Console.WriteLine ("yes, no."); }            Else{Console.WriteLine ("yes, right."); } conn.        Close (); }

*** . HasRows () differs from. Read (): HasRows only relational reading of data in a database is feasible and does not perform read operations. Read is performed to see if the execution is successful. Both return a variable of a bool row. * * *

C # Connect database-Once, delete, change, check