Getting a syntax error when trying to join two tables - mysql

Question

I have created the following tables:
USER TABLE
user_id (primary key)
account_created (date)
email (varchar)
usage_count (number)
PRODUCT TABLE
product_id (primary key)
product (varchar) (values include “iPhone”, “Android”, “Windows”)
users_supported (number) (users supported notes: some phones can support group calls up to 1000 users, some can only support normal calls of 2 users)
USAGE TABLE
usage_id (primary key)
product_id (foreign key)
user_id (foreign key)
usage_date (date)
purchase_call (number) (can be a 0, 2, 4, 6, or 10 min call)
usage_winnings (number) (when users use their minutes, sometimes they will randomly earn cash back)
computer_usage (binary value) (users can link the phone to a computer, and make calls through their computer, similar to google voice)
I want to write a select statement with the following constraints:
Time frame between 2014 and 2016
% of calls made for 2 users
% of purchased minutes used for only 2 users
Only in the first 30 days after a user created their account
In each year between 2014 and 2016, what percentage of calls and purchased calls were for only 2 users in each user's first 30 days after they created their account.
I have been practicing joins and what I have is:
SELECT COUNT(p.users_supported = 2)/COUNT(p.users_supported), SUM(CASE WHEN users_supported = 2 THEN us.purchase_call ELSE 0 END)/SUM(CASE WHEN users_supported <> 2 THEN us.purchase_call ELSE 0 END)
FROM USERS u
JOIN USAGE us ON u.user_id = us.user_id
JOIN PRODUCT p ON p.product_id = us.product_id
WHERE u.account_created >= '2014-01-01'
AND u.account_created <= '2016-12-31'
AND u.account_created <= u.account_created + 30
I have several errors right now - the percentages are not coming out correct and the account created with 30 days constraint is causing an error that breaks the whole query. Any suggestions would be much appreciated!

Answer 1

You did not state what database you are using...
First thing I notice is that
AND u.account_created <= u.account_created + 30
is always true. I think you want the query based on the current date like
AND u.account_created > NOW() - 30
If you are using sql server then you could use the datediff function and check for a result < 30
Since it was pointed out that you tagged this question mysql then using TIMESTAMPDIFF will work. Here is an example showing the syntax and the use of the NOW() function.
mysql> select TIMESTAMPDIFF(day,NOW(),'20161206');
+-------------------------------------+
| TIMESTAMPDIFF(day,NOW(),'20161206') |
+-------------------------------------+
| -17 |
+-------------------------------------+
1 row in set (0.04 sec)