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Cse 344 January 12th –joins.

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1 Cse 344 January 12th –joins

2 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

3 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)

4 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 ...

5 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

6 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?

7 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

8 Joins in SQL The standard join in SQL is sometimes 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

9 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?

10 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

11 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

12 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

13 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

14 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

15 (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”

16 (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

17 (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

18 (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

19 (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

20 (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

21 (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

22 (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)

23 (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

24 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

25 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?

26 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?

27 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!

28 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!

29 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

30 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

31 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

32 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

33 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

34 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

35 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

36 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

37 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

38 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

39 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?

40 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

41 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

42 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

43 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

44 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

45 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

46 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

47 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

48 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

49 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

50 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

51 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

52 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

53 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

54 Grouping and Aggregation
Purchase(product, price, quantity) Find total quantities for all sales over $1, by product.

55 Grouping and Aggregation
Product Price Quantity Bagel 3 20 1.50 Banana 0.5 50 2 10 4 Product TotalSales Bagel 40 Banana 20 First we apply the selection predicate to eliminate the third row, then we form groups of products, and then evaluate the aggregates and projection SELECT product, Sum(quantity) AS TotalSales FROM Purchase WHERE price > 1 GROUP BY product

56 Other Examples Compare these two queries: SELECT product, count(*)
FROM Purchase GROUP BY product SELECT month, count(*) FROM Purchase GROUP BY month SELECT product, sum(quantity) AS SumQuantity, max(price) AS MaxPrice FROM Purchase GROUP BY product What does it return?

57 Need to be Careful… SELECT product, max(quantity) FROM Purchase
GROUP BY product Product Price Quantity Bagel 3 20 1.50 Banana 0.5 50 2 10 4 Can’t project columns not in grouping / aggregate

58 Need to be Careful… SELECT product, max(quantity) FROM Purchase
GROUP BY product Product Price Quantity Bagel 3 20 1.50 Banana 0.5 50 2 10 4 SELECT product, quantity FROM Purchase GROUP BY product -- what does this mean? Can’t project columns not in grouping / aggregate

59 Need to be Careful… SELECT product, max(quantity) FROM Purchase
GROUP BY product Product Price Quantity Bagel 3 20 1.50 Banana 0.5 50 2 10 4 SELECT product, quantity FROM Purchase GROUP BY product -- what does this mean? Can’t project columns not in grouping / aggregate Product Max(quantity) Bagel 20 Banana 50

60 Need to be Careful… SELECT product, max(quantity) FROM Purchase
GROUP BY product Product Price Quantity Bagel 3 20 1.50 Banana 0.5 50 2 10 4 SELECT product, quantity FROM Purchase GROUP BY product -- what does this mean? Can’t project columns not in grouping / aggregate Product Max(quantity) Bagel 20 Banana 50 Product Quantity Bagel 20 Banana ??

61 Need to be Careful… SELECT product, max(quantity) FROM Purchase
Everything in SELECT must be either a GROUP-BY attribute, or an aggregate Need to be Careful… SELECT product, max(quantity) FROM Purchase GROUP BY product Product Price Quantity Bagel 3 20 1.50 Banana 0.5 50 2 10 4 SELECT product, quantity FROM Purchase GROUP BY product -- what does this mean? Can’t project columns not in grouping / aggregate Product Max(quantity) Bagel 20 Banana 50 Product Quantity Bagel 20 Banana ??

62 Grouping and Aggregation
Purchase(product, price, quantity) Find total quantities for all sales over $1, by product. SELECT product, Sum(quantity) AS TotalSales FROM Purchase WHERE price > 1 GROUP BY product How is this query processed?

63 Grouping and Aggregation
Purchase(product, price, quantity) Find total quantities for all sales over $1, by product. SELECT product, Sum(quantity) AS TotalSales FROM Purchase WHERE price > 1 GROUP BY product Do these queries return the same number of rows? Why? SELECT product, Sum(quantity) AS TotalSales FROM Purchase GROUP BY product

64 Grouping and Aggregation
Purchase(product, price, quantity) Find total quantities for all sales over $1, by product. SELECT product, Sum(quantity) AS TotalSales FROM Purchase WHERE price > 1 GROUP BY product Do these queries return the same number of rows? Why? SELECT product, Sum(quantity) AS TotalSales FROM Purchase GROUP BY product Empty groups are removed, hence first query may return fewer groups

65 Grouping and Aggregation
1. Compute the FROM and WHERE clauses. 2. Group by the attributes in the GROUPBY 3. Compute the SELECT clause: grouped attributes and aggregates. FWGS = From Where Group by Select (I made up that acronym) TM FWGS CSE au

66 1,2: From, Where FWGS Product Price Quantity Bagel 3 20 1.50 Banana
0.5 50 2 10 4 WHERE price > 1 SELECT product, Sum(quantity) AS TotalSales FROM Purchase WHERE price > 1 GROUP BY product

67 3,4. Grouping, Select FWGS Product Price Quantity Bagel 3 20 1.50
Banana 0.5 50 2 10 4 Product TotalSales Bagel 40 Banana 20 SELECT product, Sum(quantity) AS TotalSales FROM Purchase WHERE price > 1 GROUP BY product

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