checking for empty values

[php_begins]

i retrieving an adid from $_GET which is also a value retireved from a database.

 $this_adid=$_GET['adid'];
    if(empty($this_adid))
{
    $get_ad_id = mysql_query("SELECT userid FROM ads WHERE adid='$this_adid'", $con) or die("Error Getting AD ID: ".mysql_error());
   while($get_ad_id_results = mysql_fetch_assoc($get_ad_id)) { $owner_id=$get_ad_id_results['userid']; }
}

the above query works if  $this_adid returns 0 (http://www.website.com/?do=delete&adid=0&givenuserid=15773) i.e. adid is 0 in the table.

 

But it does not work if $this_adid returns null or ntohin (http://www.website.com/?do=delete&adid=&givenuserid=15773) .i.e adid is ' ' (empty) field in the databse table..

 

can someone tell me why it does not check for null or empty values properly?

[php_begins]

i still want to execute the query if the the adid field is empty or null.

in some places adid is stored as empty(there is no value in the database table.)

i still need to compare those values in the table nad execute.

Right now if the adid field is empty it does not return anything..

Note: adid is not a primary key.it can be null

[ohdang888]

well this:

" SELECT userid FROM ads WHERE adid='$this_adid' "

will ALWAYS be translated as this:

"SELECT userid FROM ads WHERE adid='' "

because its nested within an empty caluse.

 

Are there any records that have NOTHING in adid column? you should always try print_r on the results

 

[php_begins]

like i said the adid field is empty in the database table in some cases.(there is no value for adid in the table even when there are userids)

so i want to select userid from the ad table where adid=NULL or ' ')

this would still give me the userids.

But unfortunately it does not return anything..i do not know to how to check for fields tht have no value..