How to avoid duplicate record inserts in SQL Server using C# and ASP.Net

Make use of Stored Procedure

Code

            string strConnString = ConfigurationManager.ConnectionStrings["constr_sample"].ConnectionString;
            using (SqlConnection con = new SqlConnection(strConnString))
            {
                using (SqlCommand cmd = new SqlCommand("InsertUser"))
                {
                    cmd.Connection = con;
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.Parameters.AddWithValue("@UserName", "Mudassar");
                    cmd.Parameters.AddWithValue("@Password", "1234");
                    cmd.Parameters.AddWithValue("@Email", "mak@123.com");
                    con.Open();
                    bool success = Convert.ToBoolean(cmd.ExecuteScalar());
                    if (success)
                    {
                        Response.Write("User created");
                    }
                    else
                    {
                        Response.Write("User exists");
                    }
                    con.Close();
                }
            }

SQL

CREATE PROCEDURE InsertUser
	@UserName varchar(100),
	@Password varchar(100),
	@Email varchar(100)
AS
BEGIN
	SET NOCOUNT ON;

	IF EXISTS(SELECT * FROM [Login] WHERE UserName = @UserName)
	BEGIN
		SELECT 'FALSE'
	END
	ELSE
	BEGIN
		INSERT INTO [Login]
		VALUES(@UserName, @Password, @UserName)
		SELECT 'TRUE'
	END
END
GO