Question

I have tried a MySQL solution but it does not seem practical and I get a query that takes to long.

I am looking for a PHP solution to this problem:

I have inside my table rows with product data coming from 4 different sites.

I query them using some conditions and I get a result variable:

$result = mysql_query("my query");

Now, I retrieve the data like this:

while($slice = mysql_fetch_assoc($result)){
   $product_data = $slice['productdata'];
   $site     = $slice['site']; 
}

The problem is that I want to display product data by alternating the $site variable:

1. product from site 1;

2. product from site 2;

3. product from site 3;

4. product from site 4;

If all the products from site 2 have been listed, then list the other remaining products like this:

1. product from site 1;

2. priduct from site 3;

3. product from site 4;

And so on.

IMPORTANT: I am paginating the results so the solution cannot break pagination. So i need a total rows number I can paginate.

Could there be a PHP solution?

UPDATE:

$result = mysql_query("SELECT site, product FROM ".$table." WHERE my mysql conditions LIMIT ".$offset.", ".$rowsperpage."");

$rowsperpage = 20;

If site 3 has much more rows then the others, using the code would generate:

Page 1:

• Product from site 1;
• Product from site 2;
• Product from site 3;
• Product from site 1;
• Product from site 2;
• Product from site 3;
• Product from site 3;
• Product from site 3;
• …..
• until 20

Page 2:

• Product from site 1;
• Product from site 2;
• Product from site 3;
• Product from site 1;
• Product from site 2;
• Product from site 3;
• Product from site 3;
• Product from site 3;
• …..
• until 20

Page 3 would display the remaining site 3 rows:

• Product from site 3;
• Product from site 3;
• Product from site 3;
• …..
• until 20

The problem is Page 1 and Page 2 will display more site 3 products than the others.

This is because of the mysql query which has rows mixed and ordered by random. And when I call 20 of them, the sites won’t have equal number of rows.

I want to achieve something like:

Page 1:

• Product from site 1;
• Product from site 2;
• Product from site 3;
• Product from site 1;
• Product from site 2;
• Product from site 3;
• Product from site 1;
• Product from site 2;
• Product from site 3;
• …..
• until 20

Page 2:

• Product from site 1;
• Product from site 2;
• Product from site 3;
• Product from site 3;
• Product from site 2;
• Product from site 3;
• Product from site 3;
• Product from site 3;

…..
until 20

What I want to achieve works with the code only if I have the query on each paginated page without the offset and limit

Answer 1

Here’s (attempt #2) at a solution that may work for you.

After more thought and comments, it appears that using MySQL to handle pagination via LIMIT/OFFSET will not be an easy task to accomplish considering the ordering you need. That said, the pagination should be handled soley in PHP – the caveat here being that you have to load all of the MySQL results during every page load.

The idea is to build a 2D-array with each “site” as the index and each sub-array as the list of “products” for each site. After this is built, find the length of the longest list of products – that number will let us know how high we need to iterate to using this “buckets” method.

Now, iterate from 0 to the length of the longest list of products and, in a nested loop, iterate through each site. If the site doesn’t have a product for the current index, skip it; otherwise:

• If the current $offest is greater than 0, skip the current product and decrememnt $offset by 1.
• If $offset is less than or equal to 0, output the product!

Sample Code:

// define what page we're on (will probably come from $_GET)
$page = 1;

// define how many products to display per-page
$productsPerPage = 20;

// calculate the current offset based on the page-# and the #-per-page
$offset = (($page - 1) * $productsPerPage);

// get the full results from the database
$results = mysql_query("your query");
if (mysql_num_rows($results) <= $offset) {
    // the current page is too high; you could set it to the last page,
    // or loop back to page #1, display an error, etc.
    return;
}

$sites = array();
while ($row = mysql_fetch_assoc($result)) {
    if (!isset($sites[$row['site']])) {
        // initialize the products-array for this site
        $sites[$row['site']] = array();
    }
    // add this product to the array for this site
    $sites[$row['site']][] = $row['productdata'];
}

// get the largest-number of products for a given site
$maxProducts = 0;
foreach ($sites as $products) {
    if ($maxProducts == 0) {
        // set the first list of products as the "most"
        $maxProducts = count($products);
    } else if (($count = count($products)) > $maxProducts) {
        // the current list of products is larger than what we've found
        $maxProducts = $count;
    }
}

// iterate from the $siteOffset to the highest-number of products
for ($i = 0; $i < $maxProducts; $i++) {
    // iterate through each site and check if it has a product at this "level"
    foreach ($sites as $site => $products) {
        if (isset($products[$i])) {
            // there is a product for this site on this "level";
            // if we haven't reached our offset yet, skip it
            if ($offset-- > 0) continue;
            // otherwise, output it!
            echo $products[$i] . ' from site ' . $site . '<br />';
        }
    }
}