อยากทราบเงื่อนไขในการกรอกข้อมูล มาก เเละน้อย รบกวนพี่ๆ ด้วยนะครับ

<?php
	$objConnect = mysql_connect("localhost","000","000");
	$objDB = mysql_select_db("data");
	
	
       $strid = $_POST["id"]; 
       $old = $_POST["old"];
       $present = $_POST["present"];
	   
   
	/*** Check  ***/
	$strSQL = "SELECT * FROM data WHERE id = '".$strid."' ";
	$objQuery = mysql_query($strSQL);
	$objResult = mysql_fetch_array($objQuery);
	if($objResult)
	{
		$arr['StatusID'] = "0"; 
		$arr['Error'] = "id";	
		echo json_encode($arr);
		exit();
	}
	

       /*** INSERT  ***/
        $strSQL = "INSERT INTO data  (old,present)
		VALUES ('$old','$present')";


       $strid= mysql_insert_id();

  


	$objQuery = mysql_query($strSQL);
	if(!$objQuery)
	{
		$arr['StatusID'] = "0"; 
		$arr['Error'] = "Cannot save data!";	
	}
	else
	{
		$arr['StatusID'] = "1"; 
		$arr['Error'] = "";	
	}

	/**
		$arr['StatusID'] // (0=Failed , 1=Complete)
		$arr['Error'] // Error Message
	*/

	mysql_close($objConnect);
	
	echo json_encode($arr);
?>