while loop missunderstanding

please someone explain me this:

suppose i have an sql tabl containing 1 column "ID" and right now i have 5 entries in there like this:
a_1
a_2
a_4
a_5
a_6

i want to list all available id's up to a_10 .

so i wrote like this:

$query = mysql_query('select * from table');
for ($i = 1; $i <= 10; $i++) {
$index = "a_"."$i"
while ($line = mysql_fetch_array($query)) {
if ($line['id'] == $index) {
echo "$index <br>";
}
}
}

Code (markup):

I expected this should construct a_1 and go trough the while loop and if there is a_1 then list it, then it should construct a_2 and go trough the while loop again and list it, etc ..

however, the reality is that it constructs a_1 and go trough while loop, then constructs a_2 and NEVER go to while loop again .. so it goes trough the while loop only 1 time and that's all ..

after long trial and failure, i have come up with this code which works

$query = mysql_query('select * from table');
for ($i = 1; $i <= 10; $i++) {
$index = "a_"."$i"
while ($line = mysql_fetch_array($query)) {
if ($line['id'] == $index) {
echo "$index <br>";
break;
}
}
}

Code (markup):

(so i just added a "break;" in the "if" statement)

now, i still really don't understand what did i do .. why does the thing not want to go trough the "while" loop for each cyle of "for" loop ? is it because of the nature of "while" or because i use the mysql_fetch_array in "while" ? or maybe because of something else ?

can someone please explain me what hapened, and why did the "break;" command in the "if" loop solve the situation ? .. i did it, but i still don't understand ..

Thanks

 

<?php
mysql_connect('localhost', 'root', '' );
mysql_select_db( 'mysql' );

function up_to_int_from_index( $int, $index = 'a_' )
{
 	$count = 0 ;
	$returns = array( );
	
	if( !( $result = mysql_query( 'SELECT * FROM `help_keyword`' ) ) )
	{
		return !die( mysql_error( ) );
	}	
	else
	{
		while( $array = mysql_fetch_assoc( $result ) and $count <= $int )
		{	
		 	// your condition here
		 	$returns[] = $array ;
			$count++;
		}
	}
	return $returns[0] ? $returns : false ;
}

foreach( up_to_int_from_index( 20 ) as $database )
{
	echo "<pre>";
	print_r( $database );
	echo "</pre>";
}
?>

PHP:

There is no need for two loops, you are already looping use that loop to count up to the index you wanna include as the code does above .....

 

The reason for this is that it cycles through the entire results set the first time around. When you go to the while loop a second time you're already at the end of the result set and so the while loop is skipped.

 

yes, that's my best guess too ..

however, could you please explain me why did the "break;" solve my problem ? does "break;" reset the while loop to the begining or what ? i really have missunderstanding about what exactly the "break;" does in this case.

Thanks

 

Thanks for this one, but i'm having hard time understanding it i'm kinda very noob yet and need to look at this code for a long time to understand it i guess ..

if you could, it would be nice to see this with in-line explanations

Thanks!

 

function up_to_int_from_index( $int, $index = 'a_' )
{
 	// count how many times we loop, it's no good to rely on ids as one or more may be missing in consecutive order
    $count = 0 ;
    // we'll store the return array here
    $returns = array( );
    // query the database, I just used the mysql one, because its the only one available to me right now
    if( !( $result = mysql_query( 'SELECT * FROM `help_keyword`' ) ) )
    {
     	// there is an error with the query, so return false and die
        return !die( mysql_error( ) );
    }   
    else
    {	
      	// the query succeeded, so loop over an associative array of the database
      	// while count ( the number of times we looped ) is smaller than or equal to int
      	// the number of rows you want to retrieve, specified when the function is called
        while( $array = mysql_fetch_assoc( $result ) and $count <= $int )
        {   
            // heres the bit you have to do, it will contain whatever conditions you
            // have in place to detect wether you would like to return the data
            $returns[] = $array ;
            // increment the counter
            $count++;
        } // end while()
    }
    // if the return array has at least one result in it, then return it else return false.
    return $returns[0] ? $returns : false ;
}

PHP:

Hows that ??

 

Thanks!
will try to work it out

 

Hello,
If I got you right, you dont want to limit the number of rows you get. But you want to get all index values under a specified number. So suppose you have

a_1
a_4
a_6
a_10
a_20
a_7

in the table, you need to get only those whose numerical parts are below than 10 or some other number. That way you should get only

a_1
a_4
a_6
a_7
a_10

If thats what you want, here is the code for that. This also sorts the array in the end.

<?php
function getUpToLimit($limit,$index = 'a')
{
	$res = mysql_query("SELECT * FROM help_keywords");
	if(!$res)die(mysql_error());

	$res_arr = array();

	while(($data = mysql_fetch_array($res))!=FALSE)
	{
		list($row_index,$row_num) = explode("_",$data[0]);
		if($row_index == $index && $row_num <= $limit)
		{
			array_push($res_arr,$data[0]);
		}
	}
	usort($res_arr,"cmp");
	return $res_arr;
}
// Compare function used by usort
function cmp($a,$b)
{
	list($a_ind,$a_num) = explode('_',$a);
	list($b_ind,$b_num) = explode('_',$b);
	
// Return the difference
// It should be less than zero if a < b , equal to zero if a = b and greater than 0 if a > b
	return ($a_num - $b_num);
}
?>

PHP:

If you dont want to include the limit value, just change:

$row_num <= $limit

PHP:

to

$row_num < $limit

PHP:

I hope thats what you were asking for.

~
Thomas

 

Thanks guys for the coding. I am just learning php and i'll probably stick with my code as of yet since it works and i don't want to mess it up

although i see your code is much better, but right now i'm just trying to make the things work only, and not "work great" so i'm afraid of changing anything that works

however, i'm still wondering to know what did the "break;" command exactly do in my original code ? why did it help me ?

and why was the "while" looping only one time and not reseting its value ? once it goes trough the array and reaches the end of the array, it does not reset the pointer to the begining so it never goes to the while loop again .. so now the "break;" has changed the situation .. i want to know did the "break;" reset the array's pointer to begining or did it do something else that i don't imagine ?

Thanks