How can a Text box save multiple values on a button click in all different rows with same id

 <asp:textbox id="txtName" runat="server" xmlns:asp="#unknown"></asp:textbox>
<asp:button id="btnSave" runat="server" text="Save" onclick="btnSave_Click" xmlns:asp="#unknown" />

create table Test
(
 Id int,
 UserName varchar(500)
)

CREATE PROCEDURE sp_SaveValue (
	 @aintId INT
	,@astrUserName VARCHAR(500)
	)
AS
BEGIN

   CREATE TABLE #tempTable ( Id INT ,PID VARCHAR(50))
   INSERT INTO #tempTable (id, PID )
   SELECT Row AS ID ,Value AS SetValue FROM dbo.fn_SplitForOrdering(@astrUserName, ',')
   INSERT INTO Test (Id, UserName) SELECT @aintId,PID FROM #tempTable

END

CREATE FUNCTION dbo.fn_SplitForOrdering (
	@InputText VARCHAR(4000)
	,@Delimiter VARCHAR(10)
	)
RETURNS @Array TABLE (
	Row INT
	,Value VARCHAR(4000)
	)
AS
-----------------------------------------------------------  
-- returns a varchar rowset from a delimited string --  
-----------------------------------------------------------  
BEGIN
	DECLARE @Pos INT
	DECLARE @End INT
	DECLARE @TextLength INT
	DECLARE @DelimLength INT
	DECLARE @Row INT

	SET @TextLength = DataLength(@InputText)

	-- Exit function if no text is passed in  
	IF @TextLength = 0
		RETURN

	SET @Pos = 1
	SET @DelimLength = DataLength(@Delimiter)
	SET @Row = 1

	IF @DelimLength = 0
	BEGIN
		WHILE @Pos <= @TextLength
		BEGIN
			INSERT @Array (
				Row
				,Value
				)
			VALUES (
				@Row
				,SubString(@InputText, @Pos, 1)
				)

			SET @Pos = @Pos + 1
			SET @Row = @Row + 1
		END
	END
	ELSE
	BEGIN
		SET @InputText = @InputText + @Delimiter
		SET @End = CharIndex(@Delimiter, @InputText)

		WHILE @End > 0
		BEGIN
			INSERT @Array (
				Row
				,Value
				)
			VALUES (
				@Row
				,SubString(@InputText, @Pos, @End - @Pos)
				)

			SET @Pos = @End + @DelimLength
			SET @End = CharIndex(@Delimiter, @InputText, @Pos)
			SET @Row = @Row + 1
		END
	END

	RETURN
END

string strValue = txtName.Text; //Make sure you enter your value separated by comma.
       //int id = 2; //take your id from anywhere you want.

       int id = GetMaxId(); //see this method is returning a new Id.//[Edit]
       SqlConnection con = new SqlConnection(yourconnectionstring);
       SqlCommand cmd = new SqlCommand("sp_SaveValue", con);
       cmd.CommandType = CommandType.StoredProcedure;
       cmd.Parameters.AddWithValue("@aintId", id);
       cmd.Parameters.AddWithValue("@astrUserName", strValue);
       con.Open();
       cmd.ExecuteNonQuery();
       con.Close();

private int GetMaxId()
  {
      int intId = 0;
      SqlConnection con = new SqlConnection(strCon);
      SqlCommand cmd = new SqlCommand("select Max(Id) from Test", con);
      con.Open();
      SqlDataReader dr = cmd.ExecuteReader();
      if (dr.Read())
      {
          intId = int.Parse(dr[0].ToString());
      }
      return intId + 1;
  }