Save

.vscode/settings.json

@@ -17,7 +17,6 @@
   "files.autoSave": "afterDelay",
   "screencastMode.onlyKeyboardShortcuts": true,
   "terminal.integrated.fontSize": 18,
-  "workbench.activityBar.visible": true,
   "workbench.colorTheme": "Visual Studio Dark",
   "workbench.fontAliasing": "antialiased",
   "workbench.statusBar.visible": true,
@@ -36,5 +35,8 @@
       "password": "mariadb"
     }
   ],
-  "sqltools.useNodeRuntime": true
+  "sqltools.useNodeRuntime": true,
+  "githubPullRequests.ignoredPullRequestBranches": [
+    "main"
+  ]
 }

Chapter 2/Finding Duplicate Rows/Duplicate1.csv

@@ -0,0 +1,180 @@
+"CustomerID","FirstName","LastName","NUM_ORDERS"
+133,"Earl","Carter","2"
+292,"Roger","Welch","2"
+469,"Emily","Mitchell","2"
+561,"Kelly","Campbell","2"
+789,"Ronald","Grant","2"
+916,"Melissa","Rose","2"
+791,"Nancy","Graham","2"
+866,"Frank","Montgomery","2"
+971,"Pamela","Carpenter","2"
+126,"James","Howard","2"
+153,"Matthew","Jacobs","2"
+415,"Bruce","Morrison","2"
+529,"Charles","Shaw","2"
+734,"Cynthia","Howard","2"
+925,"Gary","Ferguson","2"
+555,"Sandra","Willis","2"
+653,"Frank","Hansen","2"
+666,"Alan","Stephens","2"
+717,"Catherine","Pierce","2"
+822,"Mary","Foster","2"
+846,"Julie","Mills","2"
+107,"Brian","Mcdonald","1"
+122,"Jean","Palmer","1"
+141,"Elizabeth","Jordan","1"
+157,"Sarah","Cooper","1"
+189,"Ryan","Scott","1"
+204,"Donald","Gilbert","1"
+227,"Michael","Anderson","1"
+265,"Julia","Morrison","1"
+330,"Paula","Campbell","1"
+343,"Raymond","Brooks","1"
+367,"Jonathan","Price","1"
+400,"Joseph","Hernandez","1"
+444,"Ruth","Holmes","1"
+454,"Anna","Porter","1"
+487,"Jeffrey","Robertson","1"
+513,"Debra","Johnston","1"
+538,"Terry","Hansen","1"
+592,"Tammy","Medina","1"
+624,"Johnny","Lee","1"
+658,"Betty","Johnson","1"
+669,"Carl","Arnold","1"
+678,"Samuel","Jordan","1"
+704,"Christopher","Brooks","1"
+718,"Doris","Anderson","1"
+746,"Carol","Reed","1"
+768,"Ruby","Rice","1"
+803,"Gregory","Young","1"
+811,"Paula","Lopez","1"
+830,"Paul","Ferguson","1"
+847,"Denise","Howell","1"
+862,"Antonio","Evans","1"
+895,"Carolyn","Clark","1"
+905,"Brenda","Daniels","1"
+935,"Catherine","Hart","1"
+968,"Steven","Taylor","1"
+978,"Karen","Frazier","1"
+1009,"Willie","Robinson","1"
+1065,"Teresa","Arnold","1"
+1080,"Pamela","Alvarez","1"
+108,"Nicholas","Clark","1"
+125,"Kathy","Alexander","1"
+135,"Doris","Watkins","1"
+144,"Anne","Hicks","1"
+164,"Joshua","Jordan","1"
+191,"Antonio","Freeman","1"
+210,"Norma","Ramos","1"
+228,"Jason","Rivera","1"
+268,"Anne","Campbell","1"
+302,"Deborah","Kennedy","1"
+334,"Lois","Warren","1"
+347,"Brandon","Elliott","1"
+369,"Daniel","Franklin","1"
+413,"Angela","Crawford","1"
+447,"Theresa","Ross","1"
+461,"Albert","Cunningham","1"
+482,"Andrew","Ramos","1"
+507,"Janet","Crawford","1"
+528,"Adam","Wood","1"
+544,"Patrick","Snyder","1"
+570,"Patrick","Weaver","1"
+600,"Phyllis","Thomas","1"
+633,"Michelle","Scott","1"
+660,"Virginia","Porter","1"
+670,"Sandra","Jones","1"
+693,"Steven","Schmidt","1"
+712,"Anthony","Collins","1"
+724,"Russell","Wood","1"
+751,"Paula","Gibson","1"
+778,"Earl","Peterson","1"
+804,"Deborah","Nguyen","1"
+813,"Kevin","Hughes","1"
+831,"Brian","Cunningham","1"
+849,"Randy","Dunn","1"
+898,"Henry","Chavez","1"
+911,"Bobby","Nelson","1"
+917,"Emily","Reyes","1"
+945,"Gloria","Ramos","1"
+982,"Karen","Martin","1"
+1039,"William","Harper","1"
+1066,"Matthew","Snyder","1"
+1093,"Helen","Carter","1"
+110,"Doris","Ramirez","1"
+136,"Rebecca","Graham","1"
+166,"Thomas","Henderson","1"
+193,"Barbara","Bell","1"
+211,"Benjamin","Garcia","1"
+248,"Anna","Wallace","1"
+280,"Katherine","Johnston","1"
+307,"Jack","Foster","1"
+336,"Aaron","Robertson","1"
+348,"Gloria","Marshall","1"
+371,"Melissa","Wheeler","1"
+448,"James","Lawrence","1"
+466,"Matthew","Turner","1"
+483,"Sara","Henry","1"
+509,"Bonnie","Grant","1"
+552,"Paul","Carpenter","1"
+571,"Patricia","Lopez","1"
+606,"Heather","Gardner","1"
+652,"John","Barnes","1"
+661,"Nancy","Walker","1"
+672,"Sharon","Thompson","1"
+695,"Stephen","Davis","1"
+714,"Kimberly","Moreno","1"
+752,"Arthur","Myers","1"
+782,"Barbara","Watkins","1"
+794,"George","Dunn","1"
+805,"Andrea","Young","1"
+820,"Eric","Dunn","1"
+833,"Mary","Ross","1"
+853,"Richard","Castillo","1"
+868,"John","Scott","1"
+899,"Keith","Castillo","1"
+914,"Deborah","Spencer","1"
+949,"Lois","Andrews","1"
+974,"Rose","Cooper","1"
+985,"Steven","Cooper","1"
+1043,"Walter","Henry","1"
+1067,"Jose","Nelson","1"
+1098,"Michael","Gonzalez","1"
+118,"Beverly","Meyer","1"
+128,"Randy","Gibson","1"
+139,"Brian","Mccoy","1"
+155,"Sarah","Taylor","1"
+181,"Louise","Cook","1"
+199,"Janet","Perez","1"
+225,"Jonathan","Gonzales","1"
+250,"Alice","Fisher","1"
+281,"Douglas","Dean","1"
+308,"Alice","Gutierrez","1"
+338,"Michael","Johnston","1"
+359,"Ruth","Garcia","1"
+387,"Timothy","Powell","1"
+422,"Ernest","Hanson","1"
+450,"Janice","Lopez","1"
+468,"Billy","Roberts","1"
+486,"Billy","Martinez","1"
+511,"Kenneth","Matthews","1"
+533,"Ann","Gordon","1"
+586,"Harold","Hamilton","1"
+610,"Martin","Reid","1"
+675,"Amy","Lawson","1"
+699,"Doris","Riley","1"
+743,"Kelly","Martinez","1"
+758,"Louis","Martin","1"
+783,"Brandon","Adams","1"
+798,"Lillian","Alexander","1"
+810,"Diane","Howard","1"
+859,"Mildred","Castillo","1"
+883,"Melissa","Hernandez","1"
+903,"Christina","Knight","1"
+915,"Louise","Jones","1"
+929,"Shawn","Adams","1"
+955,"Lawrence","Johnston","1"
+977,"Christopher","Brooks","1"
+1002,"Shawn","Bennett","1"
+1055,"Jesse","Franklin","1"
+1071,"Cynthia","Matthews","1"

Chapter 2/Finding Duplicate Rows/Duplicate1.sql

@@ -1,10 +1,16 @@
+-- Select the customer information and how many orders they have
 SELECT Customer.CustomerID,
-  Customer.FirstName,
+  Customer.FirstName,       
   Customer.LastName,
+  -- Total number of orders for each customer
   COUNT(1) as NUM_ORDERS
 FROM Customer
+-- Start with the Customer table, Join with the Orders table, matching each customer to their orders
   JOIN Orders ON Customer.CustomerID = Orders.CustomerID
-GROUP BY Customer.CustomerID,
+-- Group rows so that each customer is one line in the result
+-- Required because we've using count()
+  GROUP BY Customer.CustomerID,
   Customer.FirstName,
   Customer.LastName
+-- Sort the result by number of orders (Highest first)
 ORDER BY NUM_ORDERS DESC

Chapter 2/Finding Duplicate Rows/Duplicate2.csv

@@ -0,0 +1,10 @@
+"FirstName","LastName","-- Number of rows for each (FirstName, LastName) Combination
+        COUNT(1)"
+"Brandon","Murray","2"
+"Carolyn","Welch","2"
+"Christopher","Brooks","2"
+"Cynthia","Greene","2"
+"Frances","Jones","2"
+"Lori","Harris","2"
+"Randy","Gonzales","2"
+"Randy","Parker","2"

Chapter 2/Finding Duplicate Rows/Duplicate2.sql

@@ -1,4 +1,9 @@
-SELECT FirstName, LastName, COUNT(1)
+SELECT  FirstName,
+        LastName,
+        -- Number of rows for each (FirstName, LastName) Combination
+        COUNT(1)
 FROM Customer
-GROUP BY FirstName, LastName
+GROUP BY  FirstName,
+          LastName
+          -- Only keep groups where the count is greater than 1
 HAVING COUNT(1) > 1

Chapter 2/Finding Duplicate Rows/Duplicate3.sql

@@ -1,15 +1,22 @@
-SELECT FirstName,
+-- Select customer identity details and count how many times
+-- each unique combination of these fields appears
+SELECT 
+  FirstName,  
   LastName,
   Address,
   City,
   State,
   Zipcode,
-  COUNT(1)
+  COUNT(1)  -- number of rows that share the exact same values
 FROM Customer
-GROUP BY FirstName,
+GROUP BY 
+  FirstName,
   LastName,
   Address,
   City,
   State,
   Zipcode
-HAVING COUNT(1) > 1
+-- Keep only the groups that appear more than once.
+-- In other words, only return customers where *all six fields*
+-- are duplicated across multiple rows.
+HAVING COUNT(1) > 1;

Chapter 2/Finding Duplicate Rows/Duplicate4.csv

@@ -0,0 +1,17 @@
+"CustomerID","FirstName","LastName"
+704,"Christopher","Brooks"
+977,"Christopher","Brooks"
+508,"Randy","Gonzales"
+651,"Randy","Gonzales"
+557,"Cynthia","Greene"
+650,"Cynthia","Greene"
+601,"Lori","Harris"
+888,"Lori","Harris"
+394,"Frances","Jones"
+501,"Frances","Jones"
+152,"Brandon","Murray"
+559,"Brandon","Murray"
+234,"Randy","Parker"
+894,"Randy","Parker"
+403,"Carolyn","Welch"
+1070,"Carolyn","Welch"

Chapter 2/Finding Duplicate Rows/Duplicate4.sql

@@ -0,0 +1,9 @@
+SELECT c.CustomerID, c.FirstName, c.LastName
+FROM Customer c
+JOIN (
+    SELECT FirstName, LastName
+    FROM Customer
+    GROUP BY FirstName, LastName
+    HAVING COUNT(*) > 1
+) d ON d.FirstName = c.FirstName AND d.LastName = c.LastName
+ORDER BY c.LastName, c.FirstName, c.CustomerID;

Chapter 2/Finding Inaccurate Data Values/CheckOrderTotal.sql

@@ -1,8 +1,19 @@
-SELECT OrderItem.OrderId,
-  Orders.TotalDue,
-  SUM(Price * Quantity) as NewTotalDue
+-- Select order-level information and recalculate totals from items
+SELECT
+  OrderItem.OrderId,                   -- the ID of the order
+  Orders.TotalDue,                     -- the total amount stored in the Orders 
+  SUM(Price * Quantity) as NewTotalDue -- new total, calculated by summing each
+-- product's price X quantity
+-- Start from the OrderItem table (contains line items of each order)
 FROM OrderItem
-  JOIN Product ON OrderItem.ProductID = Product.ProductID
-  JOIN Orders ON OrderItem.OrderID = Orders.OrderID
-GROUP BY OrderItem.OrderId,
-  Orders.TotalDue
+-- Bring in product information, to get the Price for each item
+  JOIN Product
+    ON OrderItem.ProductID = Product.ProductID
+-- Bring in order-level information (e.g. stored TotalDue)
+  JOIN Orders
+    ON OrderItem.OrderID = Orders.OrderID
+-- Group results so that each order is represented once
+-- Required because we're using SUM() across multiple order items
+GROUP BY
+  OrderItem.OrderId,
+  Orders.TotalDue;

Selfstudy/SelectLastNameAndOrderID.sql

@@ -0,0 +1,6 @@
+SELECT LastName,
+  OrderId
+FROM Customer
+-- Join the Orders table to the Customer table
+  JOIN Orders 
+  on Customer.CustomerID = Orders.CustomerId;