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March 30th – intro to joins

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1 March 30th – intro to joins
Cse 344 March 30th – intro to joins

2 Administrative minutiae
Online Quizzes First quiz out Due next Friday (11:00 pm) Coding HW Due next Wednesday (11:30 pm) HW2 out next Wednesday Office hours Listed on course website

3 Demo 1 What operations should we expect SQLite (or any DBMS) to support just on what we know right now? create table insert into select delete from What sorts of inputs do these functions need to have? create table: table name, schema insert into: table name, tuple select: table name, attributes delete from: table name, condition

4 Demo 1 Common Syntax CREATE TABLE [tablename] ([att1] [type1], [att2] [type2]…); INSERT INTO [tablename] VALUES ([val1],[val2]…); SELECT [att1],[att2],… FROM [tablename] WHERE [condition] DELETE FROM [tablename] WHERE [condition]

5 Demo 1

6 Discussion Two other operations we want to support
ALTER TABLE: Adds a new attribute to the table UPDATE: Change the attribute for a particular tuple in the table. Common Syntax ALTER TABLE [tablename] ADD [attname] [atttype] UPDATE [tablename] SET [attname]=[value]

7 Discussion Two other operations we want to support
ALTER TABLE: Adds a new attribute to the table UPDATE: Change the attribute for a particular tuple in the table. Common Syntax ALTER TABLE [tablename] ADD [attname] [atttype] UPDATE [tablename] SET [attname]=[value] WHERE [condition]

8 Demo 2

9 Discussion Tables are NOT ordered they are sets or multisets (bags)
Tables are FLAT No nested attributes Tables DO NOT prescribe how they are implemented / stored on disk This is called physical data independence

10 Discussion Tables may not be ordered, but data can be returned in an order with the ORDER BY modifier

11 Discussion Tables may not be ordered, but data can be returned in an order with the ORDER BY modifier Whew, today’s been a lot of coding... I know what you’re thinking…

12 Theory break

13 Theory break We can think of accessing information through queries as some combination of functions

14 Theory break We can think of accessing information through queries as some combination of functions Consider a table of UW students (with all relevant info):

15 Theory break We can think of accessing information through queries as some combination of functions Consider a table of UW students (with all relevant info): How would we need to get the birth year of all UWBW students from California? 1953 Boston Globe – “Hepster Lingo”

16 Theory break We can think of accessing information through queries as some combination of functions Consider a table of UW students (with all relevant info): How would we need to get the birth year of all UWBW students from California? Think of the file as a set of tuples

17 Theory break We can think of accessing information through queries as some combination of functions Consider a table of UW students (with all relevant info): How would we need to get the birth year of all UWBW students from California? Think of the file as a set of tuples Find the set of UWBW students and the set of students from California; Find the intersection of these sets, return just the year from the birthday values of this set

18 Theory break We can think of accessing information through queries as some combination of functions Consider a table of UW students (with all relevant info): How would we need to get the birth year of all UWBW students from California? Think of the file as a set of tuples Find the set of UWBW students and the set of students from California; Find the intersection of these sets, return just the year from the birthday values of this set What does this return?

19 Theory break We can think of accessing information through queries as some combination of functions Consider a table of UW students (with all relevant info): How would we need to get the birth year of all UWBW students from California? Think of the file as a set of tuples Find the set of UWBW students and the set of students from California; Find the intersection of these sets, return just the year from the birthday values of this set What does this return? Years, but with many duplicates. Even though sets don’t allow duplicates, the objects are unique.

20 Theory Break If we only want to return unique elements, we can use the DISTINCT modifier Even if we hide some attributes from the output, the data is all still there. When we select a subset of the attributes, this function is called a projection

21 Theory Break This was all for a single table.
Data models specify how our data are stored and how the data are related Need to utilize these relations, or the database was pointless This involves a JOIN

22 Join: Intro The JOIN is the way we indicate in a query how multiple tables are related. Example, if we want all of the products and their relevant company information, we need to join those two tables. The result of the join is all of the relevant information from both tables Join occurs based on the join condition. This allows us to access information that comes from multiple tables

23 Retrieve all Japanese products that cost < $150
Product(pname, price, category, manufacturer) Company(cname, country) Joins in SQL pname price category manufacturer MultiTouch 199.99 gadget Canon SingleTouch 49.99 photography Gizom 50 GizmoWorks SuperGizmo 250.00 cname country GizmoWorks USA Canon Japan Hitachi Retrieve all Japanese products that cost < $150 Joins differ from selection in that we have join predicates that relate two attributes (rather than a single attribute with a constant)

24 Retrieve all Japanese products that cost < $150
Product(pname, price, category, manufacturer) Company(cname, country) Joins in SQL pname price category manufacturer MultiTouch 199.99 gadget Canon SingleTouch 49.99 photography Gizom 50 GizmoWorks SuperGizmo 250.00 cname country GizmoWorks USA Canon Japan Hitachi Retrieve all Japanese products that cost < $150 Joins differ from selection in that we have join predicates that relate two attributes (rather than a single attribute with a constant) SELECT pname, price FROM Product, Company WHERE ...

25 Retrieve all Japanese products that cost < $150
Product(pname, price, category, manufacturer) Company(cname, country) Joins in SQL pname price category manufacturer MultiTouch 199.99 gadget Canon SingleTouch 49.99 photography Gizom 50 GizmoWorks SuperGizmo 250.00 cname country GizmoWorks USA Canon Japan Hitachi Retrieve all Japanese products that cost < $150 Joins differ from selection in that we have join predicates that relate two attributes (rather than a single attribute with a constant) SELECT pname, price FROM Product, Company WHERE manufacturer=cname AND country='Japan' AND price < 150

26 Retrieve all USA companies that manufacture “gadget” products
Product(pname, price, category, manufacturer) Company(cname, country) Joins in SQL pname price category manufacturer MultiTouch 199.99 gadget Canon SingleTouch 49.99 photography Gizom 50 GizmoWorks SuperGizmo 250.00 cname country GizmoWorks USA Canon Japan Hitachi Retrieve all USA companies that manufacture “gadget” products Gill is not shown! Why?

27 Retrieve all USA companies that manufacture “gadget” products
Product(pname, price, category, manufacturer) Company(cname, country) Joins in SQL pname price category manufacturer MultiTouch 199.99 gadget Canon SingleTouch 49.99 photography Gizom 50 GizmoWorks SuperGizmo 250.00 cname country GizmoWorks USA Canon Japan Hitachi Retrieve all USA companies that manufacture “gadget” products Gill is not shown! Why? Why DISTINCT? SELECT DISTINCT cname FROM Product, Company WHERE country='USA' AND category = 'gadget' AND manufacturer = cname

28 Joins in SQL The standard join in SQL is called an inner join
Each row in the result must come from both tables in the join Sometimes we want to include rows from only one of the two table: outer join

29 Retrieve employees and their sales
Employee(id, name) Sales(employeeID, productID) Inner Join Employee id name 1 Joe 2 Jack 3 Jill Sales employeeID productID 1 344 355 2 544 Retrieve employees and their sales Jill is not shown! Why?

30 Retrieve employees and their sales
Employee(id, name) Sales(employeeID, productID) Inner Join Employee id name 1 Joe 2 Jack 3 Jill Sales employeeID productID 1 344 355 2 544 Retrieve employees and their sales Jill is not shown! Why? SELECT * FROM Employee E, Sales S WHERE E.id = S.employeeID

31 Retrieve employees and their sales
Employee(id, name) Sales(employeeID, productID) Inner Join Employee id name 1 Joe 2 Jack 3 Jill Sales employeeID productID 1 344 355 2 544 Retrieve employees and their sales Jill is not shown! Why? SELECT * FROM Employee E, Sales S WHERE E.id = S.employeeID id name empolyeeID productID 1 Joe 344 355 2 Jack 544

32 Retrieve employees and their sales
Employee(id, name) Sales(employeeID, productID) Inner Join Employee id name 1 Joe 2 Jack 3 Jill Sales employeeID productID 1 344 355 2 544 Jill is missing Retrieve employees and their sales Jill is not shown! Why? SELECT * FROM Employee E, Sales S WHERE E.id = S.employeeID id name empolyeeID productID 1 Joe 344 355 2 Jack 544

33 Retrieve employees and their sales
Employee(id, name) Sales(employeeID, productID) Inner Join Employee id name 1 Joe 2 Jack 3 Jill Sales employeeID productID 1 344 355 2 544 Jill is missing Retrieve employees and their sales Alternative syntax Jill is not shown! Why? SELECT * FROM Employee E INNER JOIN Sales S ON E.id = S.employeeID id name empolyeeID productID 1 Joe 344 355 2 Jack 544

34 Retrieve employees and their sales
Employee(id, name) Sales(employeeID, productID) Outer Join Employee id name 1 Joe 2 Jack 3 Jill Sales employeeID productID 1 344 355 2 544 Jill is present Retrieve employees and their sales Jill is not shown! Why? SELECT * FROM Employee E LEFT OUTER JOIN Sales S ON E.id = S.employeeID id name empolyeeID productID 1 Joe 344 355 2 Jack 544 3 Jill NULL

35 (Inner) joins Product(pname, price, category, manufacturer) Company(cname, country) -- manufacturer is foreign key to Company SELECT DISTINCT cname FROM Product, Company WHERE country='USA' AND category = 'gadget' AND manufacturer = cname We already gone through this in the last lecture, just that they have not heard of the term “inner”

36 (Inner) joins SELECT DISTINCT cname FROM Product, Company
WHERE country='USA' AND category = 'gadget' AND manufacturer = cname Product Company pname category manufacturer Gizmo gadget GizmoWorks Camera Photo Hitachi OneClick cname country GizmoWorks USA Canon Japan Hitachi Here they will see an example of how inner join works

37 (Inner) joins SELECT DISTINCT cname FROM Product, Company
WHERE country='USA' AND category = 'gadget' AND manufacturer = cname Product Company pname category manufacturer Gizmo gadget GizmoWorks Camera Photo Hitachi OneClick cname country GizmoWorks USA Canon Japan Hitachi

38 (Inner) joins SELECT DISTINCT cname FROM Product, Company
WHERE country='USA' AND category = 'gadget' AND manufacturer = cname Product Company pname category manufacturer Gizmo gadget GizmoWorks Camera Photo Hitachi OneClick cname country GizmoWorks USA Canon Japan Hitachi

39 (Inner) joins SELECT DISTINCT cname FROM Product, Company
WHERE country='USA' AND category = 'gadget' AND manufacturer = cname Product Company pname category manufacturer Gizmo gadget GizmoWorks Camera Photo Hitachi OneClick cname country GizmoWorks USA Canon Japan Hitachi pname category manufacturer cname country Gizmo gadget GizmoWorks USA

40 (Inner) joins SELECT DISTINCT cname FROM Product, Company
WHERE country='USA' AND category = 'gadget' AND manufacturer = cname Product Company pname category manufacturer Gizmo gadget GizmoWorks Camera Photo Hitachi OneClick cname country GizmoWorks USA Canon Japan Hitachi

41 (Inner) joins SELECT DISTINCT cname FROM Product, Company
WHERE country='USA' AND category = 'gadget' AND manufacturer = cname Product Company pname category manufacturer Gizmo gadget GizmoWorks Camera Photo Hitachi OneClick cname country GizmoWorks USA Canon Japan Hitachi

42 (Inner) joins SELECT DISTINCT cname FROM Product, Company
WHERE country='USA' AND category = 'gadget' AND manufacturer = cname SELECT DISTINCT cname FROM Product, Company WHERE country='USA' AND category = 'gadget' AND manufacturer = cname SELECT DISTINCT cname FROM Product JOIN Company ON country = 'USA' AND category = 'gadget' AND manufacturer = cname These are totally equivalent, just different syntax. You will see why we need another syntax in a sec (for outer joins)

43 (Inner) Joins for x1 in R1: for x2 in R2:
SELECT x1.a1, x2.a2, … xm.am FROM R1 as x1, R2 as x2, … Rm as xm WHERE Cond for x1 in R1: for x2 in R2: for xm in Rm: if Cond(x1, x2…): output(x1.a1, x2.a2, … xm.am) Formally, what is the semantics of joins? It’s actually the same as the following program x1, x2, xm are called TUPLE VARIABLES, they range over every tuple in R1, R2, … You don’t have to use the “.” syntax if it is clear which relation’s a1, a2, ... Am you are referring to Each relation is bound to a variable, and the dot expression iterates through the tuple in each relation, checking whether it should be output or not This is called NESTED LOOP SEMANTICS Note that as we said in the last lecture, SQL is DECLARATIVE in the sense that we didn’t prescribe how join, select, etc are executed. Other ways to execute joins are totally possible, and we will see that in a week or so. This is called nested loop semantics since we are interpreting what a join means using a nested loop

44 Another example Product(pname, price, category, manufacturer) Company(cname, country) -- manufacturer is foreign key to Company Retrieve all USA companies that manufacture products in both ‘gadget’ and ‘photography’ categories

45 Another example Product(pname, price, category, manufacturer) Company(cname, country) -- manufacturer is foreign key to Company Retrieve all USA companies that manufacture products in both ‘gadget’ and ‘photography’ categories SELECT DISTINCT z.cname FROM Product x, Company z WHERE z.country = ’USA’ AND x.manufacturer = z.cname AND x.category = 'gadget’ AND x.category = 'photography; Does this work?

46 Another example Product(pname, price, category, manufacturer) Company(cname, country) -- manufacturer is foreign key to Company Retrieve all USA companies that manufacture products in both ‘gadget’ and ‘photography’ categories SELECT DISTINCT z.cname FROM Product x, Company z WHERE z.country = ’USA’ AND x.manufacturer = z.cname AND (x.category = 'gadget’ OR x.category = 'photography); What about this?

47 Need to include Product twice!
Another example Product(pname, price, category, manufacturer) Company(cname, country) -- manufacturer is foreign key to Company Retrieve all USA companies that manufacture products in both ‘gadget’ and ‘photography’ categories SELECT DISTINCT z.cname FROM Product x, Product y, Company z WHERE z.country = ’USA’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname AND x.category = 'gadget’ AND y.category = 'photography; Need to include Product twice!

48 Self-Joins and Tuple Variables
Find USA companies that manufacture both products in the ‘gadgets’ and ‘photo’ category Joining Product with Company is insufficient: need to join Product, with Product, and with Company When a relation occurs twice in the FROM clause we call it a self-join; in that case we must use tuple variables (why?) Why? Because we need to disambiguate which table each attribute comes from!

49 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; Product Company pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan

50 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; Product Company x pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan

51 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; Product Company x pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan y

52 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; z Product Company x pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan y

53 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; z Product Company x pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan y

54 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; z Product Company x pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan y

55 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; z Product Company x pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan y

56 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; z Product Company x pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan y

57 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; z Product Company x pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan y x.pname x.category x.manufacturer y.pname y.category y.manufacturer z.cname z.country Gizmo gadget GizmoWorks MultiTouch Photo USA

58 Self-joins SELECT DISTINCT z.cname
FROM Product x, Product y, Company z WHERE z.country = ‘USA’ AND x.category = ‘gadget’ AND y.category = ‘photo’ AND x.manufacturer = z.cname AND y.manufacturer = z.cname; z Product Company x pname category manufacturer Gizmo gadget GizmoWorks SingleTouch photo Hitachi MultiTouch Photo cname country GizmoWorks USA Hitachi Japan y x.pname x.category x.manufacturer y.pname y.category y.manufacturer z.cname z.country Gizmo gadget GizmoWorks MultiTouch Photo USA

59 Outer joins Product(name, category)
Purchase(prodName, store) -- prodName is foreign key SELECT Product.name, Purchase.store FROM Product, Purchase WHERE Product.name = Purchase.prodName There is no match for those products in the purchase table. We want to include products that are never sold, but some are not listed! Why?

60 Outer joins Product(name, category)
Purchase(prodName, store) -- prodName is foreign key SELECT Product.name, Purchase.store FROM Product LEFT OUTER JOIN Purchase ON Product.name = Purchase.prodName

61 SELECT Product.name, Purchase.store FROM Product JOIN Purchase ON
Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Question about WHERE

62 SELECT Product.name, Purchase.store FROM Product JOIN Purchase ON
Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz

63 SELECT Product.name, Purchase.store FROM Product JOIN Purchase ON
Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Name Store Gizmo Wiz Output

64 SELECT Product.name, Purchase.store FROM Product JOIN Purchase ON
Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Name Store Gizmo Wiz Output

65 SELECT Product.name, Purchase.store FROM Product JOIN Purchase ON
Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Name Store Gizmo Wiz Output

66 SELECT Product.name, Purchase.store FROM Product JOIN Purchase ON
Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Name Store Gizmo Wiz Output

67 SELECT Product.name, Purchase.store FROM Product JOIN Purchase ON
Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Name Store Gizmo Wiz Camera Ritz Output

68 SELECT Product.name, Purchase.store FROM Product JOIN Purchase ON
Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Name Store Gizmo Wiz Camera Ritz Output

69 SELECT Product.name, Purchase.store FROM Product JOIN Purchase ON
Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Name Store Gizmo Wiz Camera Ritz Output

70 SELECT Product.name, Purchase.store
FROM Product LEFT OUTER JOIN Purchase ON Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Name Store Gizmo Wiz Camera Ritz Output

71 SELECT Product.name, Purchase.store
FROM Product LEFT OUTER JOIN Purchase ON Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Name Store Gizmo Wiz Camera Ritz OneClick NULL Output

72 SELECT Product.name, Purchase.store
FROM Product FULL OUTER JOIN Purchase ON Product.name = Purchase.prodName Product Purchase Name Category Gizmo gadget Camera Photo OneClick ProdName Store Gizmo Wiz Camera Ritz Phone Foo Name Store Gizmo Wiz Camera Ritz OneClick NULL Foo Output

73 Outer Joins Left outer join: Right outer join:
Include tuples from tableA even if no match Right outer join: Include tuples from tableB even if no match Full outer join: Include tuples from both even if no match In all cases: Patch tuples without matches using NULL tableA (LEFT/RIGHT/FULL) OUTER JOIN tableB ON p General syntax of joins

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