MySQL Query to find customers who have ordered two specific products

Question

I'm having trouble coming up with a query that will find all customers who have purchased both PROD1 and PROD2.

Here's a pseudo-query that kind of looks like what I want to do: (obviously this wouldn't work)

SELECT COUNT(DISTINCT userid) 
  FROM TRANSACTIONS 
 WHERE product_id = 'prod1' 
   AND product_id = 'prod2'

So basically I'm trying to get a count of the number of distinct userids that have a transaction in the transactions table for both product_id ' prod1 ' and ' prod2 '. Each transaction is stored in a row in the transactions table.

Answer 1

SELECT userid
  FROM TRANSACTIONS
 WHERE product_id in ('prod1', 'prod2')
GROUP BY userid
HAVING COUNT(DISTINCT product_id) = 2

Answer 2

I do this type of query in the following way:

SELECT COUNT(DISTINCT t1.userid) AS user_count
  FROM TRANSACTIONS t1
  JOIN TRANSACTIONS t2 USING (userid)
 WHERE t1.product_id = 'prod1' 
   AND t2.product_id = 'prod2';

The GROUP BY solution shown by @najmeddine also produces the answer you want, but it doesn't perform as well on MySQL. MySQL has a hard time optimizing GROUP BY queries.

You should try both queries, analyzing the optimization with EXPLAIN , and also run some tests and time the results given the volume of data in your database.

Answer 3

(Added new options below using the additional information provided by the user)

Try

SELECT * FROM Customers WHERE 
 EXISTS (SELECT * FROM Purchases WHERE ProductID = 'PROD1' AND CustID = Customers.CustID)
 AND
 EXISTS (SELECT * FROM Purchases WHERE ProductID = 'PROD2' AND CustID = Customers.CustID)

Or

SELECT * FROM Customers WHERE 
 CustID IN (SELECT CustID FROM Purchases WHERE ProductID = 'PROD1')
 AND
 CustID IN (SELECT CustID FROM Purchases WHERE ProductID = 'PROD2')

Or

SELECT UserID FROM Transactions WHERE ProductID = 'PROD1'
 AND EXISTS (SELECT * FROM Transactions WHERE UserID = T1.UserID 
  AND ProductID = 'PROD2')

Or

SELECT UserID FROM Transactions WHERE ProductID = 'PROD1'
 AND UserID IN (SELECT UserID FROM Transactions WHERE ProductID = 'PROD2')

Answer 4

This is an Access answer based on the infamous Northwind sample db. You should be abe to translate that in mySql quite easily.

SELECT o.CustomerID, Sum([ProductID]='Prod1') AS Expr1, Sum([productid]='Prod1') AS Expr2
FROM Orders AS o INNER JOIN [Order Details] AS d ON o.OrderID = d.OrderID
GROUP BY o.CustomerID
HAVING (((Sum([ProductID]='Prod1'))<>0) AND ((Sum([productid]='Prod1'))<>0));

Answer 5

SELECT COUNT(DISTINCT userId)
FROM(
  SELECT userId
  FROM transactions
  WHERE product = 'PROD1'
  INTERSECT
  SELECT userId
  FROM transactions
  WHERE product = 'PROD2');

The query creates two intermediate tables, one which contains userId of customer who bought PROD1 and another identical table for those who bought PROD2. The intersection operator returns a table which contains only rows found in both previous tables, ie those who bought both products.

Answer 6

Example for sakila db:

SELECT R.customer_id, GROUP_CONCAT(I.film_id) 
FROM sakila.rental R 
RIGHT OUTER JOIN sakila.inventory I ON R.inventory_id = I.inventory_id 
WHERE I.film_id IN (22,44) GROUP BY R.customer_id HAVING COUNT(*) = 2