Beginning SQL

2. The film club chairperson also wants to know how many repeat orders each customer placed
with the salesperson. The SQL to do this is shown below:
SELECT SalesPerson.SalesPersonId,
SalesPerson.FirstName,
SalesPerson.LastName,
MemberDetails.MemberId,
MemberDetails.FirstName,
MemberDetails.LastName,
COUNT(*) - 1
FROM (Orders INNER JOIN MemberDetails
ON Orders.MemberId = MemberDetails.MemberId)
INNER JOIN SalesPerson
ON Orders.SalesPersonId = SalesPerson.SalesPersonId
GROUP BY SalesPerson.SalesPersonId,
SalesPerson.FirstName,
SalesPerson.LastName,
MemberDetails.MemberId,
MemberDetails.FirstName,
MemberDetails.LastName
HAVING COUNT(Orders.MemberId) > 1
ORDER BY SalesPerson.SalesPersonId;
How It Works
First, you need to think about what the question involves. Basically, it involves counting how many
times a customer has ordered from the same salesperson. If the customer makes repeat orders from the
same salesperson, then display that record in the results.
Now you need to work out where the data to answer the question comes from. Details about orders are
found in the Orders table. Start simple and create a SELECT list that obtains the SalesPersonId and
MemberId — the customer who placed the order:
SELECT SalesPersonId, MemberId
FROM Orders;
This basic query gives the following results:
SalesPersonId MemberId
2 7
2 4
2 9
2 7
2 7
2 10
2 4
2 4
Advanced Queries
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