Detecting MySQL NULL in PHP

I have this function, which takes some SQL and returns an HTML table:


function table_sql_result($sql) {

   $str = "<table>";

   $result = mysql_query($sql);
   while ($row = mysql_fetch_assoc($result)) {
      if (!$keys) {
         $keys = array_keys($row);
         $str .= "<tr>";
         foreach ($keys as $key) {
            $str .= "<th>$key</th>";
         $str .= "</tr>";
      $str .= "<tr>";
      foreach ($row as $field) {
         switch ($field) {
         case NULL: $field = "NULL"; break; // This is catching empty strings, too!
         case "": $field = "&nbsp;"; break;
         default: $field = htmlentities($field); break;

         $str .= "<td>$field</td>";
      $str .= "</tr>";

   return $str."</table>";



Here’s the problem: I’m getting “NULL” for every empty value in the result. Considering the fact that PHP NULL is different than MySQL NULL, I’d like PHP to print “NULL” when it sees a field containing MySQL NULL, and " " when it sees a field with an empty string (“”). How would I do this?

My problem lies in that I can’t figure out how to detect MySQL NULL reliably. is_null() isn’t working.

the problem isn’t mysql, or even is_null(). it’s your case statement. you’re trying to, but can’t do this:

switch ($x) {
    //do something

which translates to this:

if ($x == NULL) {
  // do something

and if you read the editor’s note at the very bottom of the php manual page for is_null() you’ll see why.

instead detecting NULL values in php try to detect them im MySQL:

select if( field IS NULL,'custom_null_text',field)as field from table;

this works like this:
if field is NULL you can write some custom_text …or just plain ‘NULL’ or something else, and parse it later in PHP.

That would be ideal, but it doesn’t adapt well to my function (see first post).

So there is no way of telling the difference between a NULL field value and an empty string once you’ve queried the database into a PHP result?

I think this is already answered in longneck’s post. Just read it again. :wink:

…which also offers a solution to your problem.

if ($x === NULL) {
  // do something

Is this the solution?


Yes, it was. Thanks for the suggestion.