数据库SQL和CSHARP

大家好，我要一个程序，在那里我可以编辑用户，删除用户，搜索用户，创建用户，但我不知道如何使编辑和搜索代码......这是我有这么远......

//create user

 private void button3_Click(object sender, EventArgs e)

 {

     if (!string.IsNullOrWhiteSpace(textBox4.Text))

     {

         Datahandler.dbOpen();

 



         string query = "SELECT * FROM Usertable WHERE (name = '" + textBox4.Text + "')";

         SqlDataReader reader = Datahandler.SqlReader(query);

 

         if (!reader.Read())

         {

             var md5 = new MD5CryptoServiceProvider();

             byte[] origninalBytes = ASCIIEncoding.Default.GetBytes("Lav Mig Om!!");

             byte[] md5bytes = md5.ComputeHash(origninalBytes);

             string md5string = BitConverter.ToString(md5bytes).Replace("-", "");

 

             reader.Close();

             Datahandler.query("INSERT INTO usertable (name, password) Values ('" + textBox4.Text + "', '" + md5string + "')");

             MessageBox.Show("Bruger Oprettet");

         }

         else

         {

             MessageBox.Show("Brugerern eksisterer allerede!");

             reader.Close();

         }

         Datahandler.dbClose();

         textBox4.Clear();

     }

     else

         MessageBox.Show("Skriv noget i tekstboksen, \nf酶r du pr酶ver at lave en bruger.");

 }

 

 //delete user

 private void button4_Click(object sender, EventArgs e)

 {

     if (!string.IsNullOrWhiteSpace(textBox4.Text))

     {

         Datahandler.dbOpen();

 

         string query = "DELETE Usertable WHERE (name = '" + textBox4.Text + "')";

         Datahandler.query(query);

         Datahandler.dbClose();

     }

     else

         MessageBox.Show("Indtast et navn f酶r du \npr酶ver p氓 at slette en bruger");

 }

USE [TESTDB]

GO

/****** Object:  Table [dbo].[test]    Script Date: 12/07/2011 13:43:47 ******/

SET ANSI_NULLS ON

GO

SET QUOTED_IDENTIFIER ON

GO

SET ANSI_PADDING ON

GO

CREATE TABLE [dbo].[test](

	[slno] [int] NOT NULL,

	[name] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,

	[password] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,

 CONSTRAINT [PK_test] PRIMARY KEY CLUSTERED 

(

	[slno] ASC

)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]

) ON [PRIMARY]

 

GO

SET ANSI_PADDING OFF