How can I retrieve the latest row for each unique seller in a table using Laravel Eloquent?

Retrieving the Latest Rows with Max Created_at Using Laravel Eloquent

In Laravel Eloquent, retrieving the latest rows for each unique field can be achieved through a comprehensive approach. In a given table that tracks sales, where each entry includes fields such as id, seller_id, amount, and created_at, the objective is to retrieve the most recent row for each distinct seller_id.

Retrieving the Latest Row for a Specific Seller

To obtain the latest row for a specific seller, Laravel Eloquent offers a straightforward method:

<code class="php">$sales = Snapshot::where('seller_id', '=', 15)
    ->orderBy('created_at', 'DESC')
    ->first();</code>

This query selects all records from the Snapshot table where seller_id equals 15, orders them in descending order based on created_at, and retrieves the first row, effectively returning the latest sale for that seller.

Retrieving the Latest Row for Each Seller

Extending this approach to retrieve the latest row for each individual seller necessitates a more advanced strategy. The following SQL query accomplishes this task:

<code class="sql">select s.*
from snapshot s
left join snapshot s1 on s.seller_id = s1.seller_id
and s.created_at < s1.created_at
where s1.seller_id is null

In this query, the subquery s1 selects records based on the condition s.created_at < s1.created_at, which ensures that only records where subsequent rows have a later created_at timestamp are included. The outer query then selects all rows from the main table s that have no matching rows in the subquery, effectively isolating the latest records for each seller_id.

Implementing the Query in Laravel Eloquent

To implement this query using Laravel Eloquent, the query builder method can be utilized:

<code class="php">DB::table('snapshot as s')
  ->select('s.*')
  ->leftJoin('snapshot as s1', function ($join) {
        $join->on('s.seller_id', '=', 's1.seller_id')
             ->whereRaw(DB::raw('s.created_at < s1.created_at'));
   })
  ->whereNull('s1.seller_id')
  ->get();</code>

This query replicates the functionality of the SQL query by performing a left join between the snapshot table and a subquery (s1) that identifies later rows for each seller_id. The whereNull condition filters out rows that have subsequent rows, leaving only the latest record for each seller_id. Executing this query returns a collection of the most recent sales for each unique seller in the table.

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