Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource

[Mattys067]

Hi there, I am getting weird error on my site. the error is above in the subject and here is the code:

code:

function get_username($user_id){
$query = "select * from registered_users where id=".$user_id;
$result = mysql_query($query);
--> if(mysql_num_rows($result) == 1){
$row = mysql_fetch_array($result);
if($row['display_real_names']=="N"){
return $row['username'];
}else{
if($row['m_initial']==0){
$row['m_initial'] = "";
}
$name = $row['f_name']." ".$row['m_initial']." ".$row['l_name'];
if(trim($name)==""){
return $row['username'];
}else{
return $name;
}
}
}else{
return "-NA-";
}
}

the error stems from the line marked with the -->

Thanks in advanced!

[Nightfire]

Usually means you're having a problem with your query.

[boonzie]

I'm not sure here, so if I'm totaly lost please forgive me... :-)

I was looking at your query: $query = "select * from registered_users where id=".$user_id;

Isn't the last " in wrong place? Shouldn't it be: $query = "select * from registered_users where id='$user_id'"; instead?

[raf]

The quoting is correct. an id is normally a numerical fields so no need to enclose the value in single quotes, and he is just concatenating the sql-string and the variable, which is fine.

Try changing the code to

$query = "select * from registered_users where id=".$user_id;
$result = mysql_query($query) or die("Nightfire was right. There is something wrong with my query !\n
executed query = " . $query . "\nError =" . mysql_error());
if(mysql_num_rows($result) == 1){ 

[boonzie]

OK, I see...

I have never seen the quoting like that before. Are there any differenses in performance, security or something else when writning like that instead of how I wrote, or is it just two ways of doing the same thing?
I have also seen other ways of quoting in the forums here. Are there a "best" way of doing it?

Must say it's very educating to hang around here...
Thanks for your work guys

[Feyd]

In PHP, when double quoting anything, PHP will look through what is quoted for anything to parse. When using single quotes, PHP does not look for anything to parse, so from a technical perspective, single quotes (when used properly) reduce load on the parser and thus render output faster. Though this is not something most humans would notice (except for in massively large scripts, but that has issues of its own). Many people simply double quote everything in the SQL select statement and add single quotes as needed, though some people (like myself) find it better to break out what needs to be parsed and what doesn't:

$query = 'select * from registered_users where id=' . $user_id . ' LIMIT 1'; 

[raf]

Originally posted by Feyd
...some people (like myself) find it better to break out what needs to be parsed and what doesn't
[/php]

I completely agree. Always break out and concatenate.
I always use single quotes (since i break out for variables and other parsed code), with one exception --> the sql-statements. Becasuse inside an sql statement, you often use single quotes ('), and you can include single quotes inside a doublequoted string, without needing to escape them.
so you can do

$sql="select var1 from table where var2='test'";
which i find more elegant and better readable then
$sql='select var1 from table where var2=\'test\'';
+ it allows untreated cut and paste just like that so you can run it inside a db-front to check it out

[firepages]

add some error checking to let mysql tell you whats wrong , you may not want to die() in production code, but whilst developing its priceless.

<?php
$result = mysql_query($query) or die( "$query\n" . mysql_error() ) ;
?>

[boonzie]

I see.
I must confess that I have never really understood the difference in ' and " in php, but now it starts to get clearer.
Another quotation that I don't understand is the \", when shall I use that?
I also have difficulties when I want to echo out a string with both html and some variables in php, and I guess that it is the quotation that I don't can figure out. If I would like to create a row in a table by echo a string like:
<tr><td>$var1</td><td>$var2</td><tr>
How shall I write that?
Is it also possible to mix javascript and php like that? I would like to use javascript to output an alert saying things like errormessages and that submitted files have been successfully uploaded and stuff like that. I would also like to have the texts as defined constants to be able to translate them in different languages. How shall I write that, if it's possible?

[raf]

Originally posted by boonzie
I see.
I must confess that I have never really understood the difference in ' and " in php, but now it starts to get clearer.
Another quotation that I don't understand is the \", when shall I use that?

You use it when you want to, print a " inside a doubl-quoted string. Like

echo ("<a href=\"foobar.php\" title=\"whatever\">test</a>"); 

But i then use

echo ('<a href="foobar.php" title="whatever">test</a>'); 

Originally posted by boonzie
I also have difficulties when I want to echo out a string with both html and some variables in php, and I guess that it is the quotation that I don't can figure out.

either

echo ("<a href=\"$urlsent\" title=\"$urlsenttitle\">test</a>"); 

or what i would use

echo ('<a href="'. $urlsent .'" title="' . $urlsenttitle . '">test</a>'); 

If you look at the colourcoding then you'll see why. But the realadvantages is that you seperate parsed and non parsed echoed code (see previous posts). If you write valid code (--> always use double quoted values for html attributes) then you can echo out a complete html page by just putting echo(' '); arrounf it.

Originally posted by boonzie
If I would like to create a row in a table by echo a string like:
<tr><td>$var1</td><td>$var2</td><tr>
How shall I write that?

echo ("<tr><td>$var1</td><td>$var2</td><tr>"); 

or what i woul use

echo ('<tr><td>' . $var1 . '</td><td>' . $var2 . '</td><tr>'); 

Originally posted by boonzie
Is it also possible to mix javascript and php like that? I would like to use javascript to output an alert saying things like errormessages and that submitted files have been successfully uploaded and stuff like that.

You can include it just like regular HTML. The same quotingrules apply.

Originally posted by boonzie
I would also like to have the texts as defined constants to be able to translate them in different languages. How shall I write that, if it's possible?

No idea what you mean. Best start a new thread for this since you all allready hijacking this one and that question is a complete new one.

[boonzie]

Thank you for your answers, they have really helped me to start understand the quotation issues. I'll have to poke around with it for a while, and then I might get back to you.

Sorry for hijacking the thread, I just got so carried away...

I'll try to get more diciplined in the future