How to display default post with get method? - php

Question

I want to get an id from browser and display some pictures from the database.
If there is no "display2.php?productid=" found, then I want to display default image.
How can I do that?
Here is my code;
$sql = "SELECT * FROM productlist where productid=".$_GET['productid'];
$result = $mysqli->query($sql);
while($myRow = $result->fetch_array())
{
if(null !==($_GET['productid']==$myRow["productid"])){
echo "<img src=".$myRow["productid"].">";
}
else {
echo "<img src="SELECT productimage FROM productlist where productid = 1;">";
}
}
Now I will make it easier to explain for you...
Check this out;
//This part works without any problem
$sql = "SELECT * FROM productlista where productid=".$_GET['productid'];
$result = $mysqli->query($restwo);
while($myRow = $resulttwo->fetch_array())
{
if(null !==($_GET['productid']==$myRow["productid"])){
echo "<img src=".$myRow["productimage"].">";
}
//This part below (that should be default) does not work...
if (!$_GET){
echo "hello world"; }

Answer 1

Asaph pointed out SQL injection. You should bind the parameter (google it), or at the minimum do this:
$defaultImage = "SELECT * FROM productlist WHERE imageSrc != '' OR IS NOT NULL ORDER BY productid DESC LIMIT 1";
// run the query, get the result, create a variable with default image...
$defaultImageSrc = ''; // what you get from the query result
$_GET['productid'] = preg_replace('#[^0-9]#', '', $_GET['productid']);
$sql = "SELECT * FROM productlist where productid=".$_GET['productid'];
$result = $mysqli->query($sql);
while($myRow = $result->fetch_array()) {
if(!$myRow['imageSrc']) $myRow['imageSrc'] = $defaultImageSrc;
echo '<img src="'.$path.'">';
}

Answer 2

If you want either $_GET['productid'] or the max(productid) when $_GET['productid'] is not set, you can use a ternary to change your sql query
$productid = ! empty($_GET['productid']) ? " WHERE productid = ".(int)$_GET['productid'] : " ORDER BY productid DESC LIMIT 1";
$sql = "SELECT * FROM productlist".$productid
$result = $mysqli->query($sql);
while($myRow = $result->fetch_array())
{
echo "<img src=".$myRow["productimage"].">";
}
so if isset($_GET['productid']) your query would be
SELECT * FROM productlist WHERE productid = (int)$_GET['productid']
but if not the default would be
SELECT * FROM productlist ORDER BY productid DESC LIMIT 1