php error i dont understand

archer_coal

here is the error
Warning: mysql_result(): Unable to jump to row 1 on MySQL

here is the code im using.

$connect = mysql_connect($host, $user, $pass) or die("could not connect to server"); 
    $db_select = mysql_select_db($database) or die("could not select the database");

$sql = "SELECT username FROM $table2 WHERE user_id ='".$postid0."' and '".$postid1."' and '".$postid2."' and '".$postid3."' and '".$postid4."'";
		$result = mysql_db_query($database,$sql);

if (!$result || mysql_num_rows($result) < 1) {
			print mysql_error() . ' ERROR - SELECT note query failed for PosterID! ';
		}


  $col=0;
$rows=mysql_num_rows($result);
	for ($i=0; $i<4; $i++) {
	$arr[$i]=mysql_result($result,$i,$col);	
	$name0 = $arr[0];
	$name1 = $arr[1];
	$name2 = $arr[2];
	$name3 = $arr[3];
	$name4 = $arr[4];

}

i have a display tag in the web page the looks like <? =$name0?> and so forth. The variables $postid0 -2-3-4 etc have proven to be valid and therefor not the source of my problem.
Any ideas?
I'm sort of new to this so it's probably somthing stupid on my part.
Thanks in advance.

Mike

laserlight

the problem lies in your SELECT query.

I think the reason is that you're thinking "user id equal to this and that and something else", and directly translating it into SQL.

You would have to do a comparison like "user id equal to this and user id equal to that and user id equal to something else".

archer_coal

user_id is the field name in the table
i tested this code using just one variable and it worked
its when i add several '".$postid0."' and '".$postid1."' etc
that i get the error.

laserlight

actually, come to think of it, the logic of the SQL statement probably is wrong too.

You should use OR, not AND.
With AND, assuming the user_id are unique (and they should be), no rows will be returned since no row can possibly match 2 user_ids at once.

A possible query would be:

$sql = "SELECT username FROM $table2 
	WHERE user_id='$postid0' OR
	user_id='$postid1' OR
	user_id='$postid2' OR
	user_id='$postid3' OR
	user_id='$postid4'";

archer_coal

But i want all of the results for all the variables listed OR would only give me the first match right?

laserlight

I dont think so, I think that SQL doesnt use lazy evaluation of such expressions.

I suggest that you test it out.
If indeed there is lazy evaluation, then an alternative is to loop through an array of $postidN with the select statement.

stolzyboy

laserlight is correct, you want to select something where it is equal to something OR something else OR something else again

that will give you results when it matches any of the three conditions, if you use AND, that will mean it has to match ALL of the conditions

archer_coal

The error is gone when using OR instead of AND but the results are completely wrong. Almost random it seems. What exactly does OR do in this situation?
Maybe i should clarify what i'm trying to do.
I have 2 tables.
One table i pull "post_id" from and load the results into an array of $postid variables and close the connection.
This has been tested and works great.

Next connection.
I want to pull the field "username" from table 2 where the username = each item in the $postid array. Resulting in several usernames.

Is there a better what to do it than listing each $postid variable in the select statement?