How can I make sub query in laravel eloquent?

Question

When I use db raw, it works

My query is using db raw like this :

$products = DB::select(DB::raw('SELECT * 
                FROM (
                    SELECT a.*, b.name AS store_name, b.address
                    FROM products a
                    JOIN stores b ON b.id = a.store_id
                    WHERE a.category_id = '.$category_id.'
                    ORDER BY a.total_sold DESC, a.updated_at DESC
                    LIMIT '.$num.'
                ) AS product
                GROUP BY store_id'));

It works. But I want to change it use laravel eloquent

I try like this :

$products = Product::where('category_id', '=', $category_id)
     ->with('store')
     ->groupBy('store_id')
     ->orderBy('total_sold','desc')
     ->orderBy('updated_at', 'desc')
     ->take($num)
     ->get();

It also works. But orderBy updated_at not executed

How can I solve it?

Answer 1

It seems to me that you are using group by incorrectly. Even if you retrieved correct results for the query before it looks to me that it was by chance anyway. Group by should be used to aggregate query results and get aggregated column values. By choosing columns which are not actually aggregated can be dangerous if used incorrectly.

From the Mysql docs for version 5.6:

MySQL extends the standard SQL use of GROUP BY so that the select list can refer to nonaggregated columns not named in the GROUP BY clause. This means that the preceding query is legal in MySQL. You can use this feature to get better performance by avoiding unnecessary column sorting and grouping. However, this is useful primarily when all values in each nonaggregated column not named in the GROUP BY are the same for each group. The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate. Furthermore, the selection of values from each group cannot be influenced by adding an ORDER BY clause. Result set sorting occurs after values have been chosen, and ORDER BY does not affect which values within each group the server chooses.

Additionally as of MySql 5.7.5 the default SQL mode includes ONLY_FULL_GROUP_BY flag which will:

Reject queries for which the select list, HAVING condition, or ORDER BY list refer to nonaggregated columns that are neither named in the GROUP BY clause nor are functionally dependent on (uniquely determined by) GROUP BY columns.

For educational purposes you should be able to achieve the exact same query with Laravel like this (untested and without the use of table aliases), but I would avoid using it:

$subQuery = Products::selectRaw('products.*, stores.name as store_name, stores.address')
    ->join('stores', 'stores.id', '=', 'products.store_id')
    ->where('products.category_id', '=', $category_id)
    ->orderBy('products.total_sold', 'DESC')
    ->orderBy('products.updated_at', 'DESC')
    ->take($num)

$products = DB::table(DB::raw('(' . $subQuery->toSql() . ') t'))
    ->groupBy('store_id')
    ->setBindings($subQuery->getBindings())
    ->get();

But to me it seems that what you're trying to do is get all the stores together with products in your desired category. So the most Laravel solution would probably be something like:

Stores::with(['products' => function($productsQuery) use ($category_id) {
    // This limits all the retrieved products to the provided category
    $productsQuery
        ->where('category_id', '=', $category_id)
        ->orderBy('total_sold', 'DESC')
        ->orderBy('updated_at', 'DESC');
}])->whereHas('products', function($productsQuery) use ($category_id) {
    // This makes sure that the store actually has at least one product from the category
    $productsQuery->where('category_id', '=', $category_id);
})->get();

I might have made wrong assumptions by looking at your query but it doesn't make much sense at the moment... I would start from there anyway.