Visual Basic.net: Insert data into sql Database and Solve Violation of PRIMARY KEY

 

:Source code

Imports System.Data.SqlClient

Public Class Form4

    Dim con1 As SqlConnection = New SqlConnection("Data Source=.;Initial Catalog=users;Integrated Security=True")

    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

        con1.Open()

        Dim cmd2 As New SqlCommand("Select name1,username1 from table1 where username1=@username1", con1)

        cmd2.Parameters.AddWithValue("@username1", TextBox2.Text)

        Dim myreader As SqlDataReader

        myreader = cmd2.ExecuteReader()

        If (myreader.Read()) Then

            con1.Close()

            MessageBox.Show("Duplicate Username")

            con1.Close()

        Else

           con1.Close()

            Dim strsql As String

            strsql = " Insert into table1(name1,username1) Values(@name,@username)"

            Dim cmd1 As New SqlCommand(strsql, con1)

            cmd1.Parameters.AddWithValue("@name", TextBox1.Text)

            cmd1.Parameters.AddWithValue("@username", TextBox2.Text)

            con1.Open()

            cmd1.ExecuteNonQuery()

            con1.Close()

            MessageBox.Show(" insert successful")

        End If

    End Sub

End Class