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+---- CHAPTER 4 ----
+
+-- Start-of-class problems --
+USE AP
+-- Get vendors who have default terms of greater than 1 months
+SELECT VendorName, VendorID, TermsDueDays
+FROM Vendors v
+    JOIN Terms t ON t.TermsID = v.DefaultTermsID
+WHERE TermsDueDays > 30
+
+-- Get the contacts and contact updates for vendors 44, 75, and 94
+    SELECT 'Current' TYPE, VendorID, VendorName, VendorContactLName, VendorContactFName
+    FROM Vendors
+    WHERE VendorID IN (44, 75, 94)
+    -- UNION combines it as if it was one table, it can "update" the columns rather than add more
+UNION
+    SELECT 'Updates' TYPE, VendorID, '', LastName, FirstName
+    FROM ContactUpdates
+    WHERE VendorID IN (44, 75, 94)
+-- Note that ORDER BY cannot be used on UNION queries, it's applied to the final query
+ORDER BY VendorID, TYPE
+
+-- Get invoices for all vendors except those in TX
+    SELECT InvoiceID
+    FROM Invoices
+    -- Returns the query except for the stuff the matches the EXCEPT's query
+EXCEPT
+    SELECT VendorID
+    FROM Vendors
+    WHERE VendorState = 'TX'
+------------------------------------------------------
+
+-- Temporary holiday table
+-- Common use for UNIONs, can act like a makeshift table
+    SELECT '1/1/2024' DateValue, 'New Years Day' DateName
+UNION
+    SELECT '1/15/2024', 'MLK Day'
+UNION
+    SELECT '2/19/2024', 'Presidents Day'
+UNION
+    SELECT '7/4/2024', 'Fourth of July'
+
+-- stuff
+USE WideWorldImporters
+SELECT CustomerID, CustomerName, c.BuyingGroupID
+FROM Sales.Customers c
+    JOIN Sales.BuyingGroups bg ON c.BuyingGroupID = bg.BuyingGroupID
+ORDER BY CustomerName
+
+--------------------------------------------------------------------------------------------
+
+---- CHAPTER 5 ----
+
+USE AP
+-- Aggregates
+-- A function that's applied to all rows
+
+-- Count the number of invoices vendor 123 has
+-- it doesn't matter which column, so * is fine
+SELECT COUNT(*)
+FROM Invoices
+WHERE VendorId = 123
+
+-- How many invoices in 2019
+SELECT COUNT(*) TotalInvoices
+FROM Invoices
+WHERE YEAR(InvoiceDueDate) = 2019
+
+-- MIN, MAX
+-- returns the smallest and largest things
+-- can't mix and match aggregate functions with other stuff, this doesn't work
+SELECT VendorID, MIN(InvoiceTotal) SmallestInvoice, MAX(InvoiceTotal) LargestInvoice
+FROM Invoices
+WHERE YEAR(InvoiceDueDate) = 2020
+
+-- sum, average, min, and max invoice totals
+SELECT SUM(InvoiceTotal) SumOfInvoices, AVG(InvoiceTotal) AvgInvoice, MIN(InvoiceTotal) SmallestInvoice, MAX(InvoiceTotal) LargestInvoice
+FROM Invoices