Using PHP to display semi-random images?

Question

Hello,
I'm looking for help using PHP and MySQL to generate semi-random images on my web site. Here's what I'm trying to do: I have 60 images, but I only want to display 16 at a time (for examlpe http://artisdead.net/antelopegardens.php).
The way I imagine this is, the design has 16 image placeholders. I want Placeholder 1 (the first image) to randomally pull record ID 1, 2, or 3 from the SQL database, while Placeholder 2 pulls record ID 4-6, etc. It's important that one of the first 3 images displays first, while one of the second 3 images displays next, etc.
I've found various ways to randomize all the images, but I'm not understanding how to constrain the randomization the way I'm looking to. Any help would be greatly appreciated. Thanks in advance.

Answer 1

Alamo_Melt wrote:
 The way I imagine this is, the design has 16 image placeholders. I want Placeholder 1 (the first image) to randomally pull record ID 1, 2, or 3 from the SQL database, while Placeholder 2 pulls record ID 4-6, etc. It's important that one of the first 3 images displays first, while one of the second 3 images displays next, etc.
Before offering a possible solution, I should point out that your plan has a minor flaw. If you display only 16 images, and want the random choice to come from incremental sets of three, the maximum number you can have in your set is 48. The final 12 images will never be selected. For 60 images, you need 20 placeholders. The alternative is to have a total set of 64 images, and make the random choice come from incremental sets of four images.
With that caveat, here's how I would do it. The primary keys of your records might not be consecutive, particularly if records are deleted and new ones added, so it might be a good idea to have a separate column with consecutive numbers from 1 to the the maximum. To select random numbers from incremental groups of three, use the following:
$id = array();
$min = 1;
$max = 3;
for ($i = 0; $i < 16; $i++) {
  // generate random number from current set
  $id[$i] = mt_rand($min, $max);
  // increment the minimum and maximum numbers for the next set
  $min += 3;
  $max += 3;
// join the selected values as a comma-separated string
$vals = implode(',', $id);
$sql = "SELECT image FROM images WHERE id IN ($vals)";
// excecute the SQL query