[RESOLVED] Compare Current Row with Previous Rows

[bronzino]

My table Pages_CSS looks like this:

Key int(11)
ClassID text
Content longtext

The query would look something like this:

$query_Style = "SELECT ClassID, Content FROM Pages_CSS";
$Style = mysql_query($query_Style);
$row_Style = mysql_fetch_assoc($Style);

ClassIDs will be repeated in the table. Content might be repeated as well. I want the output to have each Content grouped under ClassID, without ClassIDs being repeated. In other words, I want it formatted like this:

.ClassID1
Content
Content

.ClassID2
Content
Content

Another forum member suggested that I:

compar[e] the value of the current row's ClassID attribute to the row that you previously outputted. In order to access the latter, you simply need to store it in a temporary variable before the end of the loop and use that stored value for the comparison.

I realize though, that I can't just compare the current row with the previous row. I need to compare the current row with all previous echoed rows. Something like this in a "while" loop:

if(($AnyPreviousEchoedRow['ClassID'])==($CurrentRow['ClassID'])) 
{ $ClassID='';} 
else $ClassID=$CurrentRow['ClassID'];
echo $ClassID;

I think what I need here is an array based on what ClassIDs have already been outputted. Can someone confirm whether that's the case?

Thanks for any help.

[bradgrafelman]

bronzino wrote:

I need to compare the current row with all previous echoed rows

Why? If you're ordering the results, you can be guarenteed that when you reach a different ClassID that you haven't seen it before, and that when you're done with it and the next ClassID appears then you won't see it again.

EDIT: Except now I see that you lost the ORDER BY. So.. any reason why you created a new thread for a duplicate issue and went backwards in the process of doing so?

[bronzino]

bradgrafelman;10982380 wrote:

Why? If you're ordering the results, you can be guarenteed that when you reach a different ClassID that you haven't seen it before, and that when you're done with it and the next ClassID appears then you won't see it again.

EDIT: Except now I see that you lost the ORDER BY. So.. any reason why you created a new thread for a duplicate issue and went backwards in the process of doing so?

Whoa, slow down, Brad. I just didn't put it in there. I'm not abandoning it. And I was asking a question that I thought was legitimately different from the first one.

Now I'm turning over in my head why I do not need to compare all previous rows instead of just the last one. If my data were like this:

ClassID1
ClassID2
ClassID3
ClassID4
ClassID1

And in the current loop, ClassID is ClassID1, and the previous one was ClassID4, then it wouldn't properly strike ClassID1 if it had already been outputted in previous rows - if I follow the earlier advice.

[bronzino]

Wait - it would be this:

ClassID1
ClassID1
ClassID2
ClassID3
ClassID4

Yes, yes. I am seeing it now.

[bronzino]

And here is how I got the comparison going:

<?php
  $previousClassID = '';
  ?>
  <?php do { ?>
  <?php
        if ($row_Style['ClassID'] != $previousClassID) {
          echo '<br/>'.$row_Style['ClassID']; 
        } else {
          echo '&nbsp;';
        }
        $previousClassID = $row_Style['ClassID'];
   ?>
   <?php 
   	   echo '<br/>'.$row_Style['Content']; 
   ?>

  <?php } while ($row_Style = mysql_fetch_assoc($Style));
?>