C# .NET - how to check username exists in database using c#.net window application

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If you are using SQL Server as your database, you can do the following:

SqlConnection sqlConnection = new SqlConnection("YourConnectionString");
SqlCommand sqlCommand = ("", sqlConnection);
int userCount;

sqlCommand.CommandType = CommandType.Text;
sqlCommand.CommandText = "SELECT COUNT(*) FROM [dbo].[YourUsersTable] WHERE [UserName] = @UserName";
sqlCommand.Parameters.Add("@UserName", SqlDbType.VarChar, 20);
sqlCommand.Parameters["@UserName"] = YourUserNameHere;

sqlConnection.Open();
userCount = Convert.ToInt32(sqlCommand.ExecuteScalar());
if (userCount != 0)
   // user name exists;
sqlConnection.Close();

Regards,
http://www.sql-server-helper.com/faq/dates-p01.aspx

   

            SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename='|DataDirectory|\Database.mdf';Integrated Security=True;Connect Timeout=30;User Instance=True");

SqlCommand cmd = new SqlCommand("SELECT * FROM user where usernam="+ txtusername.Text, cn);

          cn.Open();

 

          

            int i=cmd.ExecuteNonQuery();

            if (i > 0)

            {

                MessageBox.Show("user with this name exists");

            }

            else

            {

                MessageBox.Show("user doesnot exists");

            }