MySQL query (CustomerID and dates of 1st, 2nd and 3rd purchases) - mysql

Question

I am trying to create a dashboard with customer ID and dates of 1st, 2nd and 3rd purchases. I use MySQL, Northwind db.
My query works perfectly fine for the 1st purchase, but I do not understand how to find 2nd and 3rd purchase date for each customer.
Now I'm trying to do next: 2nd_purchase_date is the next MIN(OrderDate) after 1st_purchase_date but I get following error 'Invalid use of group function'
DROP TABLE IF EXISTS t1;
CREATE TABLE t1
(
CustomerID varchar(5),
OrderDate datetime,
OrderID int,
i int
);
INSERT INTO t1(CustomerID, OrderDate, OrderID, i)
SELECT CustomerID, min(OrderDate), min(OrderID),1
FROM Orders
GROUP BY CustomerID;
INSERT INTO t1(CustomerID, OrderDate, OrderID, i)
SELECT CustomerID,min(OrderDate), min(OrderID),2
FROM Orders
WHERE min(OrderDate)
NOT IN
(
SELECT CustomerID, min(OrderDate), min(OrderID)
FROM Orders
)
GROUP BY CustomerID;
INSERT INTO t1(CustomerID, OrderDate, OrderID, i)
SELECT CustomerID,min(OrderDate), OrderID,3
FROM Orders
WHERE min(OrderDate)
NOT IN
(
SELECT CustomerID, min(OrderDate), min(OrderID) FROM Orders
)
GROUP BY CustomerID;

Answer 1

As shown in the last example here, you can use the LIMIT offset, count feature in combination with ORDER BY column ASC to select the entry with the second purchase date for a single user (with the id XXX replaced with the respective value):
SELECT CustomerID, OrderDate, OrderID
FROM Orders
WHERE CustomerID = XXX
ORDER BY OrderDate ASC
LIMIT 1, 1;
or the entry with the third purchase date:
SELECT CustomerID, OrderDate, OrderID
FROM Orders
WHERE CustomerID = XXX
ORDER BY OrderDate ASC
LIMIT 2, 1;
... and so on.
You get the first entry via
SELECT CustomerID, OrderDate, OrderID
FROM Orders
WHERE CustomerID = XXX
ORDER BY OrderDate ASC
LIMIT 0, 1;
or the equivalent:
SELECT CustomerID, OrderDate, OrderID
FROM Orders
WHERE CustomerID = XXX
ORDER BY OrderDate ASC
LIMIT 1;
This should give you the first three orders for a single customer:
SELECT CustomerID, OrderDate, OrderID
FROM Orders
WHERE CustomerID = XXX
ORDER BY OrderDate ASC
LIMIT 3;
While the following is definitely not good from a performance perspective, it should still work to give you the first three orders for each customer:
SELECT o1.CustomerID, o1.OrderDate, o1.OrderID
FROM Orders o1
WHERE o1.OrderID IN
(SELECT o2.OrderID
FROM Orders o2
WHERE o1.CustomerID = o2.CustomerID
ORDER BY o2.OrderDate ASC LIMIT 3)
ORDER BY o1.CustomerID, o2.OrderDate ASC;