PHP/MySQL group results by column - php

Question

in order to keep as few SQL statements as possible, I want to do select set from MySQL:
SELECT * FROM products WHERE category IN (10,120,150,500) ORDER BY category,id;
Now, I have list of products in following manner:
CATEGORY
- product 1
- product 2
CATEGORY 2
- product 37
...
What's the best and most efficent way to process MySQL result?
I thought something like (pseudo PHP)
foreach ($product = fetch__assoc($result)){
$products[$category][] = $product;
}
and then when outputting it, do foreach loop:
foreach($categories as $category){
foreach($products[$category] as $product){
$output;
}
}
Is this the best, or is something magical like mysql_use_groupby or something?

Answer 1

Like mluebke commented, using GROUP means that you only get one result for each category. Based on the list you gave as an example, I think you want something like this:
$sql = "SELECT * FROM products WHERE category IN (10,120,150,500) GROUP BY category ORDER BY category, id";
$res = mysql_query($sql);
$list = array();
while ($r = mysql_fetch_object($res)) {
$list[$r->category][$r->id]['name'] = $r->name;
$list[$r->category][$r->id]['whatever'] = $r->whatever;
// etc
}
And then loop through the array. Example:
foreach ($list as $category => $products) {
echo '<h1>' . $category . '</h1>';
foreach ($products as $productId => $productInfo) {
echo 'Product ' . $productId . ': ' . $productInfo['name'];
// etc
}
}

Answer 2

Nope, I think your solution is the best for this problem. It seems that what's important for you is the output later on, so you should stick with your approach.

Answer 3

Do you want to get a list of categories or actually get all products grouped into categories?
If it's the latter, best to do:
SELECT
p.product_id,
p.name,
p.category_id,
c.name AS category
FROM products p
JOIN categories c ON (c.category_id = p.category_id AND p.category_id IN (x,y,z))
Then in PHP you can go through the array (psuedo code):
$cats = array();
foreach($products as $product) {
if(!in_array($product['category'], $cats)) {
$cats[$product['category_id']] = $product['category'];
}
$cats[$product['category_id']][$product['product_id']] = $product['name'];
}
Which will leave you with $cats as an array with products sorted into it.