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

Connecting to a database

        static void Main (string[] args)        {            //sqlconnection conn = new SqlConnection ();//Instantiate            //conn. ConnectionString = "server=.; Database=mydb;uid=sa;pwd=123 ";//initialization-----can be executed with the following statement            SqlConnection conn = new SqlConnection (" server=.; Database=mydb;uid=sa;pwd=123 ");            Console.WriteLine (Conn. State);            Conn. Open ();//Opens the database connection            Console.WriteLine (Conn. State);            Conn. Close ();//Shut Down database connection            Console.WriteLine (Conn. State);                   }

Connect to a database and insert data

        static void Main (string[] args)        {            SqlConnection conn = new SqlConnection ("server=.; Database=mydb;uid=sa;pwd=123 ");            Conn. Open ();            SqlCommand cmd = new SqlCommand ();            Cmd. Connection = conn;//initialization, database cmd is connected by Conn data Object            . CommandText = "INSERT into info values (' p005 ', ' student ', ' 0 ', ' n001 ', ' 1990-02-1 ')"//"" In SQL statement            cmd. ExecuteNonQuery ();            Conn. Close ();            Console.WriteLine ("OK");        }

Connect to the database and modify the data

        public static void Main (string[] args)        {            SqlConnection conn = new SqlConnection ("server=.; Database=mydb;uid=sa;pwd=123 ");            Conn. Open ();            SqlCommand cmd = new SqlCommand ();            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)        {            SqlConnection conn = new SqlConnection ("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 void Main (string[] args)        {            SqlConnection conn = new SqlConnection ("server=.; Database=mydb;uid=sa;pwd=123 ");                        Conn. Open ();            SqlCommand cmd = conn. CreateCommand ();            Cmd.commandtext = "SELECT * from info";            SqlDataReader r = cmd. ExecuteReader ();//The query statement returns the SqlDataReader class while            (R.read ())            {                                Console.WriteLine (r[0]) with ExecuteReader. ToString () +r[1]. ToString () +r[2]. ToString ());            }            Conn. Close ();        }

Case: User Login implementation

        public static void Main (string[] arges)        {            console.write ("User name:");            String uid = Console.ReadLine ();            Console.Write ("Password:");            string pwd = Console.ReadLine ();            SqlConnection conn = new SqlConnection ("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 ("Hum, no");            }            else            {                Console.WriteLine ("Hum, 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