How do I make my own true / false return function?

Question

Hi there,

I want to make my own function which performs in a similar manner to the following actual code.. ie

if(mysql_num_rows($res) == FALSE) {

  // DO SOMETHING BECAUSE THERE ARE NO RESULTS

}

In my code, i'm repeating an SQL statement a few times around the place, and if there are results, then I go ahead and do stuff.

What I'd like to do is create my own FALSE return in my own function ie

if(my_special_function($variable) == FALSE) {

    // DO STUFF

}

Is this as simple as in my special function having something like...

function my_special_function($variable) {

   $sql = 'SELECT field FROM table WHERE something=$variable';
   $res = mysql_query($sql);

   if(mysql_num_rows($res) == FALSE) {

     return FALSE;

   } else {

     return TRUE;

   }
}

?

Answer 1

I can see a few problems.

Variable interpolation does not happen in single quotes, also its advisable to not to substitute variable directly into queries.

   $sql = 'SELECT field FROM table WHERE something=$variable';

should be

   $sql = 'SELECT field FROM table WHERE something='.mysql_real_escape_string($variable);

mysql_num_rows returns false when there is a problem, say when its parameter is not a valid resource. If you really want to check the case of "no rows returned" you need to check its value for 0

Answer 2

Yes, that is all for a function. Why don't you try such things first before asking whether it works or not?

You should add additional error checking for mysql_query and replace $sql = 'SELECT field FROM table WHERE something=$variable'; by:

$sql = 'SELECT field FROM table WHERE something='.$variable;

Answer 3

I'd revise it a bit

function my_special_function($variable) {
   $sql = "SELECT field FROM table WHERE something=$variable";
   $res = mysql_query($sql);

   if(mysql_num_rows($res)) {
     return TRUE;
   }
   return FALSE;
}

Changes

1. No need for the else { ... } as if the if evaluation is true, it won't go any further, if it isn't, then FALSE is returned.
2. Changed the if statement to if(mysql_num_rows($res)) as mysql_num_rows() will return FALSE on failure, and a number on everything else. So, if there's 0 affected rows, or an error you won't get the return TRUE.
3. Inside your $sql variable you had single quotes, the literal $variable would be passed rather than what was passed to the function

Answer 4

You can make your special function even simpler:

function my_special_function($variable)
{
   $sql = "SELECT field FROM table WHERE something='{$variable}'";
   $res = mysql_query($sql);
   return mysql_num_rows($res) > 0;
}