How to count new users in last month in SQL? - mysql

Question

I want to know how many new users we have last month, and how many of them have turned into buyers while I can not figure it out smoothly.the following is what I coded.
SELECT COUNT(DISTINCT(PRODUCT_ID))
FROM ORDER_TABLE AS O
INNER JOIN CUSTOMER_TABLE AS C
ON O.CUSTOMER_ID=C.CUSTOMER_ID
WHERE DATEDIFF(MONTH,ORDER_DATE,GETDATE())<=1
And there is another question which has confused me a lot: Which category have the highest YEAR BY YEAR growth in terms of revenue in 2016?

Answer 1

This should do it...
SELECT COUNT(Customer_ID)
FROM Customer_Table
WHERE Customer_ID IN (
SELECT Customer_ID
FROM Order_Table
)
AND DATEDIFF(MONTH, First_Visit, GETDATE()) <= 1

Answer 2

Guessing ...
This gives a list of the new users last month.
SELECT Customer_ID, Country, Gender
FROM Customer_Table
WHERE First_Visit >= (LAST_DAY(CURDATE()) + INTERVAL 1 DAY) - INTERVAL 2 MONTH
AND First_Visit < (LAST_DAY(CURDATE()) + INTERVAL 1 DAY) - INTERVAL 1 MONTH
That date range, given that today is 2017-08-14, looks like this after all the date arithmetic. That means "the calendar month immediately preceding this day."
WHERE First_Visit >= '2017-07-01'
AND First_Visit < '2017-08-01'
The Number of new visitors last month is a simple summary of that query.
SELECT COUNT(*)
FROM Customer_Table
WHERE First_Visit >= (LAST_DAY(CURDATE()) + INTERVAL 1 DAY) - INTERVAL 2 MONTH
AND First_Visit < (LAST_DAY(CURDATE()) + INTERVAL 1 DAY) - INTERVAL 1
Now, to elaborate a bit. How do we tell if a new user has purchased anything? We look in the order table. Something like this will do it.
SELECT C.Customer_ID, SUM(O.Order_Amount) Total_Order_Amount
FROM Customer_Table C
LEFT JOIN Order_Table O ON C.Customer_ID = O.Customeer_ID
WHERE First_Visit >= (LAST_DAY(CURDATE()) + INTERVAL 1 DAY) - INTERVAL 2 MONTH
AND First_Visit < (LAST_DAY(CURDATE()) + INTERVAL 1 DAY) - INTERVAL 1 MONTH
GROUP BY C.Customer_ID
This gives you a list of new customers, with a column showing how much each has ordered. So a NULL or 0 in the Total_Order_Amount column means a new customer who has never ordered anything.
Pro tip:
Incomplete and vague requirements are definitely part of stupid professor tricks. But they are also part of the world of information technology. Often a big part of a assignment, or a contract, or a project, is taking ridiculously vague requirements like the ones you've been given and refining them into something useful.