php variable null value and insert into database

[blackhorse]

Table: productsID varchar, price decimal

Get the input from a form, if price value is not numeric, then it will be NULL.

$productsID=$POST['productsID'];
$price=$POST['prince'];

$productsID=mysql_real_escape_string($productsID);

if (!is_numeric($price))
$price=NULL; //the below sql will have error.
$price="NULL"; //the below sql will be fine

$insert_sql="insert into products (productsID, price) values ('$productsID', $price);
mysql_query($insert_sql);

So my questions are

1) If I want set up the not numeric $price to NULL for my php programming usage, I will use
$price=NULL;

but

2) If I want to insert the NULL value of $price into database
I will need set up
$price="NULL"; //instead of $price=NULL;

Am I right here?

In other words, you cannot just simply insert a null value variable into database, you have to covert it to "NULL" first before insert it?

Thanks!

[ClarkF1]

Couldn't you have setup the database to have a default NULL value for that column and then you only have to insert the productID if the price is non-numeric. The NULL field is automatically created.

I think the PHP error may have been related to the lack of single quotes around $price when trying to insert a non-numeric value

if (!is_numeric($price))
{
$price=NULL; //the below sql will have error.
$insert_sql="insert into products (productsID) values ('$productsID')";
}
else
$insert_sql="insert into products (productsID, price) values ('$productsID', $price)";