What is the big O of database fetch methods?

Question

ORM

I was wondering how the database selection methods work,
i.e. if you take laravel:

User::find($id);

Or take node js: Then these methods in both laravel and node js bypass each field in the database (O (n)) or access this field , how to array element(O(1))?

db.collection('users').find({"email": email})

Answer 1

These methods neither in Laravel nor in Node bypass any fields, all the work is done by the DBMS. How exactly it does this depends on the DBMS and on the data schema.

Answer 2

If without foreach, then array_filter() can be used.
If the data is taken from the database, then why not immediately select only those where not null?

Answer 3

<?php
$array = array(
    [
        'id' => '1',
        'user_id' => 1,
        'child' => [
            [
                'id' => 1,
                'item_id' => 1,
                'project_id' => 3
                ],
             [
                'id' => 2,
                'item_id' => 2,
                'project_id' => 0
                ]
            ]
        ]
    );
    
    var_dump(array_filter($array[0]['child'], function($v, $k) {
    return $k == 'project_id' && $v != 0;
}, ARRAY_FILTER_USE_BOTH));

Result:

array(1) {
  [0]=>
  array(3) {
    ["id"]=>
    int(1)
    ["item_id"]=>
    int(1)
    ["project_id"]=>
    int(3)
  }
}