Self Join on MySql table - php

Question

So I a have some users in my database and each one of them is able to submit 'referrals' to our company. I am creating a table which shows how many referrals each user has submitted from the current month and previous month so we can track if they are an active sales rep. While I was successful in displaying the current month numbers for a given user, I have been having a hard time displaying the information from the previous month correctly. I get the number of referrals from the previous month, but it gives me the same number for each of the users.
|=========|========|==========|=============|
|user_id refer_id referals date |
|-------------------------------------------|
|1 1 mcdonalds 2017-12-19 |
|1 2 Burger King 2017-12-19 |
|1 3 Wendys 2017-12-21 |
|1 4 Arby's 2017-12-22 |
|1 5 In n' out 2018-01-02 |
|2 6 Chipotle 2018-01-03
|2 7 Carl's jr. 2018-01-04 |
|===========================================|
User 1 should have 1 referral and user 2 should have 2 referrals for the current month, which indeed works, and User 1 should have 4 referrals for the previous month, however I am getting 4 returned for each user. I would also like to condense this down into one query, but I'm not sure what type of JOIN to use, or do I even need one? I have found information on SELF JOINS and INNER JOIN and previous questions about it, but I'm not sure which to use in my case.
<table class="table table-hover">
<thead>
<tr>
<th>Sales Name</th>
<th>Current Month</th>
<th>Previous Month</th>
</tr>
</thead>
<?php
//CURRENT MONTH QUERY
$query = "SELECT user_id, COUNT(refer_id) AS refer_total
FROM table
WHERE MONTH(date) = MONTH(CURDATE()) GROUP BY user_id";
$result = mysqli_query($connection, $query);
//PREVIOUS MONTH QUERY
$query2 = "SELECT user_id, COUNT(refer_id) AS previous_total
FROM table
WHERE
YEAR(date) = YEAR(CURRENT_DATE - INTERVAL 1 MONTH) AND
MONTH(date) = MONTH(CURRENT_DATE - INTERVAL 1 MONTH) GROUP BY user_id";
$total = mysqli_query($connection, $query2);
while($values = mysqli_fetch_assoc($total)) {
$previous = $values['previous_total'];
}
while($values = mysqli_fetch_assoc($result)) {
$user_id = $values['user_id'];
$num_refer = $values['refer_total'];
echo "<tr><td>$user_id</td><td>$num_refer</td><td>$previous</td></tr>";
}
if(mysqli_num_rows < 5) {
echo "Inactive!";
}
?>
</table> <!--END TABLE-->

Answer 1

You need to group by the date as well using a date function. The only reason it appears as though the current month is correct in your results is because each user has 1 for the current month.
mysql> select user_id, date_format(date,'%Y-%m'), count(*) from test group by user_id, date_format(date,'%Y-%m');
+---------+---------------------------+----------+
| user_id | date_format(date,'%Y-%m') | count(*) |
+---------+---------------------------+----------+
| 1 | 2017-12 | 4 |
| 1 | 2018-01 | 1 |
| 2 | 2018-01 | 1 |
+---------+---------------------------+----------+
3 rows in set (0.00 sec)
actually i just realized that wasn't the format you were looking for. Something like the following should work:
mysql> select user_id,
sum(case date_format(date,'%Y-%m') when date_format(curdate(),'%Y-%m') then 1 else 0 end) as current_month,
sum(case date_format(date,'%Y-%m') when date_format(DATE_SUB(curdate(), INTERVAL 1 MONTH),'%Y-%m') then 1 else 0 end) as previous_month
from test group by user_id;
+---------+---------------+----------------+
| user_id | current_month | previous_month |
+---------+---------------+----------------+
| 1 | 1 | 4 |
| 2 | 1 | 0 |
+---------+---------------+----------------+
2 rows in set (0.00 sec)