Ado. NET Basic Learning

(keep track of your own review)

Concept

Simply understand the class used to connect to the database.

Work flow

The ①connection object is used to connect to the database.

Two ways to connect: Windows Authentication/SQL Server Authentication

 Private voidButton1_Click (Objectsender, EventArgs e) {                Try                {                                       //string Str = "Server=.;i Nitial catalog= "DB_PWMS"; integrated SECURITY=SSPI ";//Windows Authentication                    stringSTR ="server=.; Database="Db_pwms"; uid=sa;pwd=***"; // SQL Server Authentication                     //A string that declares the STR store connection database. //server=.                    Server name = Equals Local. //Initial catalog= "db_pwms" database name =db_pwms. SqlConnection conn=NewSqlConnection (STR);//declaring ObjectsConn. Open ();//Connect on                    if(Conn. State==connectionstate.open)//The State property is judged open or not{richTextBox1.Text="has been opened"; }                }                Catch{MessageBox.Show ("Connection Failed"); }        }

The ②command object is used to manipulate the database. (Three important methods: ExecuteNonQuery (), ExecuteReader (), ExecuteScalar ())

⑴ Use the ExecuteNonQuery () method as an example of update (change data)

 Private voidButton2_Click (Objectsender, EventArgs e) {SqlConnection conn=NewSqlConnection ("Server=.;i Nitial catalog=db_pwms;integrated Security=sspi"); Conn. Open ();//first, connect.            Try{SqlCommand cmd=NewSqlCommand ();//instance action item cmdCmd. Connection = conn;//Operation Conn This databaseCmd.commandtext ="Update table_1 set prices =3333 where Origin = ' homemade '";//operation of such a sentence SQL statementCmd.commandtype = CommandType.Text;//The book is so written, do not know what to do, and later know. It's OK to get rid of this sentence. Cmd. ExecuteNonQuery ();//Command object One of the three important methods, perform additions and deletions to search                inti =Convert.ToInt32 (cmd.                ExecuteNonQuery ()); Label2. Text= i +"Data Changes"; }            Catch(Exception ex) {MessageBox.Show (ex). Message); }        }

Click events (Button2)

Pre-execution database

After execution

⑵ data in various poses executescalar ()

The aggregate function of this method

	Description
AVG ()	Average
Count ()	There are several data
Max ()	Maximum Value
Min ()	Minimum value
SUM ()	And

Take count () and Max () as an example

Private void button3_click (object  sender, EventArgs e)        {
            conn = new SqlConnection ("Server=.;i Nitial catalog=db_pwms;integrated Security=sspi ");
Conn. Open ();             Try             {

string S1 = "SELECT COUNT (2) from Table_1";//Number of Tables count ()
String s2 = "Select Max (prices) from Table_1";//prices Max ()

SqlCommand cmd = new SqlCommand (s1,conn);
SqlCommand cmd1 = new SqlCommand (s2,conn);

                int i = Convert.ToInt32 (cmd. ExecuteScalar ()); // object to int type                int j = Convert.ToInt32 (cmd1. ExecuteScalar ());                 = i+" Strip data ";                 " The most expensive " + J;            }             Catch (Exception ex) {MessageBox.Show (ex). Message); }        }

Ado. NET Basic Learning