Segment purchases based on new vs returning - sql

Question

I'm trying to write a query that can select a particular date and count how many of those customers have placed orders previously and how many are new. For simplicity, here is the table layout:
id (auto) | cust_id | purchase_date
-----------------------------------
1 | 1 | 2010-11-15
2 | 2 | 2010-11-15
3 | 3 | 2010-11-14
4 | 1 | 2010-11-13
5 | 3 | 2010-11-12
I was trying to select orders by a date and then join any previous orders on the same user_id from previous dates, then count how many had orders, vs how many didnt. This was my failed attempt:
SELECT SUM(
CASE WHEN id IS NULL
THEN 1
ELSE 0
END ) AS new, SUM(
CASE WHEN id IS NOT NULL
THEN 1
ELSE 0
END ) AS returning
FROM (
SELECT o1 . *
FROM orders AS o
LEFT JOIN orders AS o1 ON ( o1.user_id = o.user_id
AND DATE( o1.created ) = "2010-11-15" )
WHERE DATE( o.created ) < "2010-11-15"
GROUP BY o.user_id
) AS t

Answer 1

Given a reference data (2010-11-15), then we are interested in the number of distinct customers who placed an order on that date (A), and we are interested in how many of those have placed an order previously (B), and how many did not (C). And clearly, A = B + C.
Q1: Count of orders placed on reference date
SELECT COUNT(DISTINCT Cust_ID)
FROM Orders
WHERE Purchase_Date = '2010-11-15';
Q2: List of customers placing order on reference date
SELECT DISTINCT Cust_ID
FROM Orders
WHERE Purchase_Date = '2010-11-15';
Q3: List of customers who placed an order on reference date who had ordered before
SELECT DISTINCT o1.Cust_ID
FROM Orders AS o1
JOIN (SELECT DISTINCT o2.Cust_ID
FROM Orders AS o2
WHERE o2.Purchase_Date = '2010-11-15') AS c1
ON o1.Cust_ID = c1.Cust_ID
WHERE o1.Purchase_Date < '2010-11-15';
Q4: Count of customers who placed an order on reference data who had ordered before
SELECT COUNT(DISTINCT o1.Cust_ID)
FROM Orders AS o1
JOIN (SELECT DISTINCT o2.Cust_ID
FROM Orders AS o2
WHERE o2.Purchase_Date = '2010-11-15') AS c1
ON o1.Cust_ID = c1.Cust_ID
WHERE o1.Purchase_Date < '2010-11-15';
Q5: Combining Q1 and Q4
There are several ways to do the combining. One is to use Q1 and Q4 as (complicated) expressions in the select-list; another is to use them as tables in the FROM clause which don't need a join between them because each is a single-row, single-column table that can be joined in a Cartesian product. Another would be a UNION, where each row is tagged with what it calculates.
SELECT (SELECT COUNT(DISTINCT Cust_ID)
FROM Orders
WHERE Purchase_Date = '2010-11-15') AS Total_Customers,
(SELECT COUNT(DISTINCT o1.Cust_ID)
FROM Orders AS o1
JOIN (SELECT DISTINCT o2.Cust_ID
FROM Orders AS o2
WHERE o2.Purchase_Date = '2010-11-15') AS c1
ON o1.Cust_ID = c1.Cust_ID
WHERE o1.Purchase_Date < '2010-11-15') AS Returning_Customers
FROM Dual;
(I'm blithely assuming MySQL has a DUAL table - similar to Oracle's. If not, it is trivial to create a table with a single column containing a single row of data. Update 2: bashing the MySQL 5.5 Manual shows that 'FROM Dual' is supported but not needed; MySQL is happy without a FROM clause.)
Update 1: added qualifier 'o1.Cust_ID' in key locations to avoid 'ambiguous column name' as indicated in the comment.

Answer 2

How about
SELECT * FROM
(SELECT * FROM
(SELECT CUST_ID, COUNT(*) AS ORDER_COUNT, 1 AS OLD_CUSTOMER, 0 AS NEW_CUSTOMER
FROM ORDERS
GROUP BY CUST_ID
HAVING ORDER_COUNT > 1)
UNION ALL
(SELECT CUST_ID, COUNT(*) AS ORDER_COUNT, 0 AS OLD_CUSTOMER, 1 AS NEW_CUSTOMER
FROM ORDERS
GROUP BY CUST_ID
HAVING ORDER_COUNT = 1)) G
INNER JOIN
(SELECT CUST_ID, ORDER_DATE
FROM ORDERS) O
USING (CUST_ID)
WHERE ORDER_DATE = [date of interest] AND
OLD_CUSTOMER = [0 or 1, depending on what you want] AND
NEW_CUSTOMER = [0 or 1, depending on what you want]
Not sure if that'll do the whole thing, but it might provide a starting point.
Share and enjoy.

Answer 3

select count(distinct o1.cust_id) as repeat_count,
count(distinct o.cust_id)-count(distinct o1.cust_id) as new_count
from orders o
left join (select cust_id
from orders
where purchase_date < "2010-11-15"
group by cust_id) o1
on o.cust_id = o1.cust_id
where o.purchase_date = "2010-11-15"