Question

Mysql or through PHP?

I have a design that calls for grouping articles by their date. The date will be a heading and all articles from the latest 10 will be grouped under each heading. The date can be anything and/or highly sporadic, the articles must be in descending order, etc.

I figure i would have to

1. retrieve the last 10 articles and put them in a multi-dimensional array like so:

   $allretrieved = array ( array ( id => a, date => b, title => c, body => d, image => e, etc.),
                           array ( id => a, date => b, title => c, body => d, image => e, etc.),
                           etc.
                   );
   

2. then group the array by using a method I don’t fully understand ( extract into another array? Would someone explain this function to me?)

   $date_groups[] = array();
   $group = '';
   
   foreach( $date_groups as $key=>$val ) {
       if($key == 'date'){
            $group = $val;
       }
   $comment_groups[$group][] = $val;
   }
   

3. and then sort the groups?

Or should I sort beforehand?

is doing it at the MySql level faster? more efficient?

EDIT: Best Method I have found for this:
Basic PHP MySQL array grouping question

Answer 1

At some point where your dataset isn’t too big, sorting with mysql should be faster if indexes are correctly added since default mysql indexes are b-tree. In your case, bringing the data and looping over it you will have a O(n) thus the sorting will take more as the data gets bigger.

I recommend you to take a look to your database schema, use explain to see how indexes are being used in the query you are running and benchmark. AGAIN: this will depend of your data.

now, for a sake of dreaming: Once your data is big enough to make the sorting too slow in mysql then you should switch something where you can sort in parallel using map-reduce or something like that, but given the nature of your post I think you are safe for now.