1. Write a SELECT statement that returns the same result set as this SELECT
statement. Substitute a subquery in a WHERE clause for the inner join.
SELECT DISTINCT VendorName
FROM Vendors JOIN Invoices
ON Vendors.VendorID = Invoices.VendorID
ORDER BY VendorName

2. Write a SELECT statement that answers this question: Which invoices have a
PaymentTotal that’s greater than the average PaymentTotal for all paid invoices?
Return the InvoiceNumber and InvoiceTotal for each invoice.

3. Write a SELECT statement that answers this question: Which invoices have a
PaymentTotal that’s greater than the median PaymentTotal for all paid invoices?
(The median marks the midpoint in a set of values; an equal number of values lie
above and below it.) Return the InvoiceNumber and InvoiceTotal for each invoice.
Hint: Begin with the solution to exercise 2, then use the ALL keyword in the
WHERE clause and code “TOP 50 PERCENT PaymentTotal” in the subquery.

4. Write a SELECT statement that returns two columns from the GLAccounts table:
AccountNo and AccountDescription. The result set should have one row for each
account number that has never been used. Use a correlated subquery introduced with
the NOT EXISTS operator. Sort the final result set by AccountNo.

5. Write a SELECT statement that returns four columns: VendorName, InvoiceID,
InvoiceSequence, and InvoiceLineItemAmount for each invoice that has more than
one line item in the InvoiceLineItems table.
Hint: Use a subquery that tests for InvoiceSequence > 1.

6. Write a SELECT statement that returns a single value that represents the sum of the
largest unpaid invoices submitted by each vendor. Use a derived table that returns
MAX(InvoiceTotal) grouped by VendorID, filtering for invoices with a balance due.

7. Write a SELECT statement that returns the name, city, and state of each vendor
that’s located in a unique city and state. In other words, don’t include vendors that
have a city and state in common with another vendor.

8. Write a SELECT statement that returns four columns: VendorName,
InvoiceNumber, InvoiceDate, and InvoiceTotal. Return one row per vendor,
representing the vendor’s invoice with the earliest date.