Efficient way to track returning users? - php

Question

I'm in the process of finding an efficient way to track returning users.
List of options I went over so far:
save (update) login count per user, per day/week/month
save (update) which users have logged in, in a Text field (bad choice?), per day/week/month
deduce returning users via other database resources (user-added records from several tables)
I think this last option is most efficient, since I won't need to create a separate logging table.
However, a logging table seems more accurate, period-wise, right?
Update:
Accuracy still has the priority for this, so I went with the first option, together with some logic in PHP.
I've opted to store the login counts per week (of the year), like: 201433.
Question: regarding the PHP code, is there a way to combine the two queries, and leave out the nested loop (efficiency)?
Database Table:
+----+--------+--------+-----------+
| id | userId | logins | year_week |
+----+--------+--------+-----------+
| 1 | 1 | 4 | 201432 |
| 2 | 1 | 3 | 201433 |
| 3 | 2 | 2 | 201433 |
+----+--------+--------+-----------+
Queries:
SELECT
userId,
SUM(logins) as total
FROM
User_Logins
GROUP BY
userId
ORDER BY
userId
-----------
// get first year_week
SELECT
userId,
year_week
FROM
User_Logins
GROUP BY
userId
ORDER BY
userId
Query results:
+--------+-------+
| userId | total |
+--------+-------+
| 1 | 7 |
| 2 | 2 |
+--------+-------+
+--------+-----------+
| userId | year_week |
+--------+-----------+
| 1 | 201432 |
| 2 | 201433 |
+--------+-----------+
PHP code:
$returningUsers = 0;
$userLogins = $this->model->firstQuery();
$userLoginWeeks = $this->model->secondQuery();
$today = new DateTime();
function weeksPassed($today, $year, $week)
{
$today->setISODate($today->format('Y'), $today->format('W'));
// year and week from user first login
$yearWeek = new DateTime();
$yearWeek->setISODate($year, $week);
$daysPassed = $today->diff($yearWeek)->days;
$weeksPassed = $daysPassed / 7;
return $weeksPassed;
}
if ($userLogins && $userLoginWeeks)
{
foreach ($userLoginWeeks as $userLoginWeek)
{
$userId = $userLoginWeek->userId;
$year_week = $userLoginWeek->year_week;
$year = (int) substr($year_week, 0, 4);
$week = (int) substr($year_week, 4);
$weeksPassed = weeksPassed($today, $year, $week);
$totalLogins = 0;
// Look up user logins from other query
foreach ($userLogins as $logins)
{
if ($logins->userId == $userId)
{
$totalLogins = $logins->total;
break;
}
}
$avgLogins = $totalLogins;
// Average calculated over weeks that have passed since first login
if ($weeksPassed > 0)
{
$avgLogins = $totalLogins / $weeksPassed;
}
// if average >= 1 per week => returning user
if ($avgLogins >= 1)
{
$returningUsers++;
}
}
}
return $returningUsers;