VALIDATION. no duplicates on column. php/mysql

programming
1

I have the following query:
select * from shoppertrack;

on column SELECTEDITEM, the result is:

g45, LDR01, TYU

I want to do some validation before adding a new item so there wont be any duplicates. I have hyperlinks that pass the variable to the page where the item is added. How would I create a script that echoes the message “Item already selected” when for example, someone selects g45?

This is what I have so far but doesn’t work:


$sessionid = session_id();

	//PREVENT DUPLICATION
	$checkSession = "SELECT sessionid FROM SHOPPERTRACK";
	if(!$checkSession){ exit("<p class='alert'>Could not get database information during duplicate prevention.</p>"); }
	$checkSessionResult = mysql_query($checkSession) or die("<p class='alert'>Could not get database information during duplicate prevention.</p>");
	while($rowSession = mysql_fetch_array($checkSessionResult))
	{
	$rowSessionid = $rowSession["sessionid"];

	//PREVENT DUPLICATION
	$check = "SELECT selecteditem FROM SHOPPERTRACK WHERE sessionid = '$sessionid'";
	if(!$check){ exit("<p class='alert'>Could not get database information during duplicate prevention.</p>"); }
	$checkResult = mysql_query($check) or die("<p class='alert'>Could not get database information during duplicate prevention.</p>");

	while($row = mysql_fetch_array($checkResult))
		{
		$productidCheck = $row["selecteditem"];
		if($productidCheck == $productid AND $sessionid == $rowSessionid)
		{ 
		$productidCheck = strtoupper($productidCheck);
		exit("<p class='alert'>Product: " . $productidCheck . " has already been added to shopping cart. Please go back and continue.</p>");
		} }
	}

	$checkSession = "SELECT * FROM SHOPPERTRACK";
	if(!$checkSession){ exit("<p class='alert'>Could not get database information during duplicate prevention.</p>"); }
	$checkSessionResult = mysql_query($checkSession) or die("<p class='alert'>Could not get database information during duplicate prevention.</p>");

	$number_of_rows = mysql_num_rows($checkSessionResult);

	while($rowSession = mysql_fetch_array($checkSessionResult))
	{
	$rowSessionid = $rowSession["sessionid"];
		if($sessionid == $rowSessionid)
		{
		$selecteditemRow = $rowSession["selecteditem"];
		$quantityRow = $rowSession["quantity"];
		$priceRow = $rowSession["PRICE"];
		
		echo "quantityRow: " . $quantityRow . "<p>";
		$quantity = 1;
		$updateSelecteditem = $selecteditemRow . ", " . $productid;
		$updateQuantity = $quantityRow . ", " . $quantity;
		$updatePrice = $priceRow . ", " . $price;
		
		echo "item: " . $updateSelecteditem . "<BR>";
		echo "quantity: " . $updateQuantity . "<BR>";
		echo "price: " . $updatePrice . "<BR>";

		$sql = "UPDATE shoppertrack SET " .
		"selecteditem = '$updateSelecteditem', " .
		"PRICE = '$updatePrice', " .
		"quantity = '$updateQuantity', " .
		"timeadded = CURTIME(), " .
		"dateadded = CURDATE() " .
		"WHERE sessionid = '$sessionid'";
		$result = mysql_db_query('magalys', $sql);
			if($result)
			{ echo("<p class='success'>62: Item successfully added to database.</p><p><a href='showCart.php?customerid=" .
			$customerid . "'>Click here to view your shopping cart.</a></p>"); }
			else { echo("<p class='alert'>Error. Please go back and try again. " . __line__ . "</p>"); }
		}
		else
		{
	$number_of_rows++;
	echo "Number of rows: " . $number_of_rows . "<p>";
	if($number_of_rows == 1)
	{
			echo("<p>INSERT</p>");
			$sql = "INSERT INTO shoppertrack SET " .
			"sessionid = '$sessionid', " .
			"selecteditem = '$productid', " .
			"customerid = '$customerid', " .
			"quantity = 1, " .
			"price = '$price', " .
			"dateadded = curdate(), " .
			"timeadded = curtime()" ;
			$result = mysql_db_query('magalys', $sql);
				if($result)
				{ echo("<p class='success'>101: Item successfully added to database.</p><p><a href='showCart.php?customerid=" .
				$customerid . "'>Click here to view your shopping cart.</a></p>"); }
				else { echo("<p class='alert'>Error. Please go back and try again.103</p>"); }
	}
	} // END WHILE
}