1. 1 Database Systems Lecture #6 Yan Pan School of Software, SYSU 2011

2. 2 Agenda Basic SQL RA…

3. 3 Recap: You are here First part of course is done: conceptual foundations You now know:  E/R Model  Relational Model  Relational Algebra (a little) You now know how to:  Capture part of world as an E/R model  Convert E/R models to relational models  Convert relational models to good (normal) forms Next:  Create, update, query tables with R.A/SQL  Write SQL/DB-connected applications

4. 4 3-minute Normalization Review 1. Q: What’s required for BCNF? 2. Q: How do we fix a non-BCNF relation? 3. Q: If As  Bs violates BCNF, what do we do? 4. Q: Can BCNF decomposition ever be lossy? 5. Q: How do we combine two relations? 6. Q: Can BCNF decomp. lose FDs? 7. Q: Why would you ever use 3NF?

5. 5 Next topic: SQL Standard language for querying and manipulating data Structured Query Language Many standards: ANSI SQL, SQL92/SQL2, SQL3/SQL99 Originally: Structured English Query Language (SEQUEL) Vendors support various subsets/extensions We’ll do Oracle/MySQL/generic  “No one ever got fired for buying Oracle.” Basic form (many more bells and whistles in addition): SELECT attributes FROM relations (possibly multiple, joined) WHERE conditions (selections) SELECT attributes FROM relations (possibly multiple, joined) WHERE conditions (selections)

6. 6 Data Types in SQL Characters:  CHAR(20)-- fixed length  VARCHAR(40)-- variable length Numbers:  BIGINT, INT, SMALLINT, TINYINT  REAL, FLOAT -- differ in precision  MONEY Times and dates:  DATE  DATETIME-- SQL Server

7. 7 “Tables” PNamePriceCategoryManufacturer Gizmo$19.99GadgetsGizmoWorks Powergizmo$29.99GadgetsGizmoWorks SingleTouch$149.99PhotographyCanon MultiTouch$203.99HouseholdHitachi Product Attribute names Table name Tuples or rows

8. 8 Simple SQL Query PNamePriceCategoryManufacturer Gizmo$19.99GadgetsGizmoWorks Powergizmo$29.99GadgetsGizmoWorks SingleTouch$149.99PhotographyCanon MultiTouch$203.99HouseholdHitachi SELECT * FROM Product WHERE category='Gadgets' Product PNamePriceCategoryManufacturer Gizmo$19.99GadgetsGizmoWorks Powergizmo$29.99GadgetsGizmoWorks “selection”

9. 9 Simple SQL Query PNamePriceCategoryManufacturer Gizmo$19.99GadgetsGizmoWorks Powergizmo$29.99GadgetsGizmoWorks SingleTouch$149.99PhotographyCanon MultiTouch$203.99HouseholdHitachi SELECT PName, Price, Manufacturer FROM Product WHERE Price > 100 Product PNamePriceManufacturer SingleTouch$149.99Canon MultiTouch$203.99Hitachi “selection” and “projection”

10. 10 A Notation for SQL Queries SELECT Name, Price, Manufacturer FROM Product WHERE Price > 100 Product(PName, Price, Category, Manfacturer) (PName, Price, Manfacturer) Input Relation Output Relation

11. Guifeng Zheng, DBMS, SS/SYSU 11 The WHERE clause Contains a boolean expression Teach literal is a test: x = y, x < y, x <= y, etc.  For numbers, they have the usual meanings  For CHARs/VARCHARs: lexicographic ordering Expected conversion between CHAR and VARCHAR  For dates and times, what you expect

12. 12 Complex RA Expressions Schema: Movies (Title, year, length, inColor, studioName, Prdcr#) Q: How long was Star Wars (1977)? Strategy: find the row with Star Wars; then project the length field TitleYearLengthinColorStudioPrdcr# Star Wars1977124TrueFox12345 M.Ducks1991104TrueDisney67890 W.World199295TrueParamount99999

13. 13 Combining operations Query: Which Fox movies were >= 100 minutes long? TitleYearLengthFilmtypeStudio Star wars1977124ColorFox Mighty ducks1991104ColorDisney Wayne’s world199285ColorParamount

14. 14 Next (parallel) topic: relational algebra Projection Selection Cartesian Product Joins: natural joins, theta joins Set operations: union, intersection, difference Combining operations to form queries Dependent and independent operations

15. 15 What is relational algebra? An algebra for relations “High-school” algebra: an algebra for numbers Algebra = formalism for constructing expressions  Operations  Operands: Variables, Constants, expressions Expressions:  Vars & constants  Operators applied to expressions  They evaluate to values AlgebraVars/constsOperatorsEval to High-schoolNumbers+ * - / etc.Numbers RelationalRelations (=sets of tupes) union, intersection, join, etc. Relations

16. 16 Why do we care about relational algebra? 1. The exprs are the form that questions about the data take  The relations these exprs cash out to are the answers to our questions 2. RA ~ more succinct rep. of many SQL queries 3. DBMS parse SQL into something like RA First proofs of concept for RDBMS/RA:  System R at IBM  Ingress at Berkeley “Modern” implementation of RA: SQL  Both state of the art, mid-70s

17. 17 Relation operators Basic operators:  Selection:   Projection:   Cartesian Product:  Other set-theoretic ops:  Union:   Intersection:  Difference: - Additional operators:  Joins (natural, equijoin, theta join, semijoin)  Renaming:   Grouping…

18. 18 Selection op Selects all tuples satisfying a condition Notation:  c (R) Examples   salary > 100000 (Employee)   name = “Smith” (Employee) The condition c can have  comparison ops:=,, , <>  boolean ops: and, or

19. 19 Selection example Select the movies at Angelica:   Theater=“Sunshine” (Showings) Masc. Fem.VillageFilm Forum Village N’hood Bad Edu. Annie Hall Title Sunshine Theater Village N’hood Bad Edu. Annie Hall Title Sunshine Theater

20. 20 Projection op Keep only certain columns Projection: op we used for decomposition  Eliminates other columns, then removes duplicates Notation:  A1,…,An (R)

21. 21 Cartesian product op Cross product again  “Cartesian Product” Each tuple in R 1 combines w/each tuple in R 2 Algebraic notation: R 1  R 2  Not actual SQL! If R1, R2 fields overlap, include both and disambiguate: R1.A, R2.A Q: Where does the name come from? Q: If R1 has n1 rows and R2 has n2, how large is R1 x R2?

22. 22 Cartesian product example StreetCity 333 Some StreetChappaqua 444 Embassy RowWashington Hillary-addresses Job Senator First Lady Lawyer Hillary-jobs StreetCityJob 333 Some StreetChappaquaSenator 444 Embassy RowWashingtonSenator 333 Some StreetChappaquaFirst Lady 444 Embassy RowWashingtonFirst Lady 333 Some StreetChappaquaLawyer 444 Embassy RowWashingtonLawyer Hillary-addresses x Hillary-jobs

23. 23 Join op Corresponds to SQL query doing cross & equality test Specifically: R 1 R 2 =  every att once (  shared atts = (R 1  R 2 ))  I.e., first compute the cross product R 1 x R 2  Next, select the rows in which shared fields agree  Finally, project onto the union of R 1 and R 2 ’s fields (remove duplicates)

24. 24 Natural join example NameStreetCity Hilary333 Some StreetChappaqua Hilary444 Embassy RowWashington BillSomewhere elseddd Addresses NameJob HilarySenator HilaryFirst Lady HilaryLawyer Jobs Addresses Jobs NameStreetCityJob Hilary333 Some StreetChappaquaSenator Hilary444 Embassy RowWashingtonSenator Hilary333 Some StreetChappaquaFirst Lady Hilary444 Embassy RowWashingtonFirst Lady Hilary333 Some StreetChappaquaLawyer Hilary444 Embassy RowWashingtonLawyer

25. 25 Natural Join R S R S= ? Unpaired tuples called dangling AB XY XZ YZ ZV BC ZU VW ZV

26. 26 Natural Join Given the schemas R(A, B, C, D), S(A, C, E), what is the schema of R S ? Given R(A, B, C), S(D, E), what is R S? Given R(A, B), S(A, B), what is R S?

27. 27 Join on arbitrary test ABC 123 678 978 BCD 234 235 7810 AU.BU.CV.BV.CD 123234 123235 1237810 67878 97878 UV U V A<D “Theta-join”

28. 28 Rename op Changes the schema, not the instance Notation:  B1,…,Bn (R)  is spelled “rho”, pronounced “row” Example:  Employee(ssn,name)    social, name) (Employee)  Or just:   (Employee)

29. 29 RA  SQL SQL SELECT  RA Projection  SQL WHERE  RA Selection  SQL FROM  RA Join/cross  Comma-separated list… SQL renaming  RA rho  More ops later Keep RA in the back of your mind…

30. 30 Next: Joins in SQL Connect two or more tables: PNamePriceCategoryManufacturer Gizmo$19.99GadgetsGizmoWorks Powergizmo$29.99GadgetsGizmoWorks SingleTouch$149.99PhotographyCanon MultiTouch$203.99HouseholdHitachi Product Company CNameStockPriceCountry GizmoWorks25USA Canon65Japan Hitachi15Japan What is the connection between them?

31. 31 Joins in SQL Product (pname, price, category, manufacturer) Company (cname, stockPrice, country) Find all products under $200 manufactured in Japan; return their names and prices. SELECT PName, Price FROM Product, Company WHERE Manufacturer=CName AND Country='Japan' AND Price <= 200 Join between Product and Company

32. 32 Joins in SQL PNamePriceCategoryManufacturer Gizmo$19.99GadgetsGizmoWorks Powergizmo$29.99GadgetsGizmoWorks SingleTouch$149.99PhotographyCanon MultiTouch$203.99HouseholdHitachi Product Company CnameStockPriceCountry GizmoWorks25USA Canon65Japan Hitachi15Japan PNamePrice SingleTouch$149.99 SELECT PName, Price FROM Product, Company WHERE Manufacturer=CName AND Country='Japan' AND Price <= 200

33. 33 Joins in SQL Product (pname, price, category, manufacturer) Company (cname, stockPrice, country) Find all countries that manufacture some product in the ‘Gadgets’ category. SELECT Country FROM Product, Company WHERE Manufacturer=CName AND Category='Gadgets'

34. 34 Joins in SQL NamePriceCategoryManufacturer Gizmo$19.99GadgetsGizmoWorks Powergizmo$29.99GadgetsGizmoWorks SingleTouch$149.99PhotographyCanon MultiTouch$203.99HouseholdHitachi Product Company CnameStockPriceCountry GizmoWorks25USA Canon65Japan Hitachi15Japan Country ?? What is the problem? What’s the solution? SELECT Country FROM Product, Company WHERE Manufacturer=CName AND Category='Gadgets'

35. 35 Joins Product (pname, price, category, manufacturer) Purchase (buyer, seller, store, product) Person(name, phone, city) Find names of Seattleites who bought Gadgets, and the names of the stores they bought such product from. SELECT DISTINCT name, store FROM Person, Purchase, Product WHERE persname=buyer AND product = pname AND city='Seattle' AND category='Gadgets'

36. 36 SQL Query Semantics Parallel assignment – all tuples Doesn’t impose any order Answer = {} for all assignments x1 in R1, …, xn in Rn do if Conditions then Answer = Answer  {(a1,…,ak)} return Answer Answer = {} for all assignments x1 in R1, …, xn in Rn do if Conditions then Answer = Answer  {(a1,…,ak)} return Answer SELECT a1, a2, …, ak FROM R1 AS x1, R2 AS x2, …, Rn AS xn WHERE Conditions SELECT a1, a2, …, ak FROM R1 AS x1, R2 AS x2, …, Rn AS xn WHERE Conditions

37. 37 SQL Query Semantics Nested loops: Answer = {} for x1 in R1 do for x2 in R2 do ….. for xn in Rn do if Conditions then Answer = Answer  {(a1,…,ak)} return Answer Answer = {} for x1 in R1 do for x2 in R2 do ….. for xn in Rn do if Conditions then Answer = Answer  {(a1,…,ak)} return Answer SELECT a1, a2, …, ak FROM R1 AS x1, R2 AS x2, …, Rn AS xn WHERE Conditions SELECT a1, a2, …, ak FROM R1 AS x1, R2 AS x2, …, Rn AS xn WHERE Conditions

38. 38 Multiple join syntaxes Old-style syntax simply lists tables separated by commas New-style makes the join explicit: Functionally equivalent to old-style, but perhaps more elegant Introduced in Oracle 8i, MySQL 3.x/4.x Older versions / other DBMSs may not support this SELECT * FROM A,B WHERE …; SELECT * FROM A,B WHERE …; SELECT * FROM A JOIN B ON … WHERE …; SELECT * FROM A JOIN B ON … WHERE …;

39. 39 New-style join types Cross joins (simplest):  FROM A CROSS JOIN B Inner joins (regular joins):  FROM A [INNER] JOIN B ON … Natural join:  FROM A NATURAL JOIN B;  Joins on common fields and merges Outer joins (later)  No dangling rows

40. 40 CROSS JOIN e.g. NameAddressGenderBirthdate Hanks123 Palm RdM01/01/60 Taylor456 Maple AvF02/02/40 Lucas789 Oak StM03/03/55 NameAddressNetworth Spielberg246 Palm Rd10M Taylor456 Maple Av20M Lucas789 Oak St30M MovieStar MovieExec

41. 41 CROSS JOIN e.g. MovieS tar.nam e MovieStar.add ress MovieSta r. Gender MovieStar.Birthdate MovieEx ec. Name MovieExec.Ad dress MovieEx ec. Networth Hanks123 Palm RdM01/01/60Spielberg246 Palm Rd10M Hanks123 Palm RdM01/01/60Taylor456 Maple Av20M Hanks123 Palm RdM01/01/60Lucas789 Oak St30M Taylor456 Maple AvF02/02/40Spielberg246 Palm Rd10M Taylor456 Maple AvF02/02/40Taylor456 Maple Av20M Taylor456 Maple AvF02/02/40Lucas789 Oak St30M Lucas789 Oak StM03/03/55Spielberg246 Palm Rd10M Lucas789 Oak StM03/03/55Taylor456 Maple Av20M Lucas789 Oak StM03/03/55Lucas789 Oak St30M Row 1 2 3 4 5 6 7 8 9 SELECT * FROM MovieStar CROSS JOIN MovieExec SELECT * FROM MovieStar CROSS JOIN MovieExec

42. 42 JOIN … ON e.g MovieSt ar.name MovieStar.addr ess MovieS tar. Gender MovieStar. Birthdate MovieExec. Name MovieExec.Add ress MovieEx ec. Networth Hanks123 Palm RdM01/01/60Spielberg246 Palm Rd10M Hanks123 Palm RdM01/01/60Taylor456 Maple Av20M Hanks123 Palm RdM01/01/60Lucas789 Oak St30M Taylor456 Maple AvF02/02/40Spielberg246 Palm Rd10M Taylor456 Maple AvF02/02/40Taylor456 Maple Av20M Taylor456 Maple AvF02/02/40Lucas789 Oak St30M Lucas789 Oak StM03/03/55Spielberg246 Palm Rd10M Lucas789 Oak StM03/03/55Taylor456 Maple Av20M Lucas789 Oak StM03/03/55Lucas789 Oak St30M Row 1 2 3 4 5 6 7 8 9 SELECT * FROM MovieStar JOIN MovieExec ON MovieStar.Name <> MovieExec.Name SELECT * FROM MovieStar JOIN MovieExec ON MovieStar.Name <> MovieExec.Name

43. 43 NATURAL JOIN MovieStar(name, address, gender, birthdate) MovieExec(name, address, networth) Natural Join syntax:  FROM MovieStar NATURAL JOIN MovieExec Results: list of movie stars who are also execs:  (Name, address, gender, birthdate, networth)

44. 44 NATURAL JOIN e.g. NameAddressGenderBirthdate Hanks123 Palm RdM01/01/60 Taylor456 Maple AvF02/02/40 Lucas789 Oak StM03/03/55 NameAddressNetworth Spielberg246 Palm Rd10M Taylor456 Maple Av20M Lucas789 Oak St30M MovieStar MovieExec NameAddressGenderBirthdateNetworth Taylor456 Maple AvF02/02/4020M Lucas789 Oak StM03/03/5530M SELECT * FROM MovieStar NATURAL JOIN MovieExec

45. 45 Another complex example People(ssn, name, street, city, state, state) Q: Who lives on George’s street? A: First, generate pairs of (renamed) people:   p1 (People) x  p2 (People) Then pick out pairs with George:   p1.name='George' (  p1 (People) x  p2 (People)) And refine to rows with George and someone else:   p1.name='George‘ AND p1.name<>p2.name (  p1 (People) x  p2 (People)) Finally, project out the names:   p2.name (  p1.name='George‘ AND p1.name<>p2.name (  p1 (People) x  p2 (People))

46. 46 Live examples Q: produce a list of employees and their bosses  What if no boss? Or no subordinate? Joins on emp, emp man:  Comma-based  Inner  Natural  Cross  Outer – left, right, full

47. 47 More live examples Inner joins require an ON clause  Like a where clause  Arbitrary boolean expression  If always true (1=1), reduces to cross join New compar op: BETWEEN  a between 5 and 10  a >= 5 and a <= 10 Q: produce a list of employees with their salary grades  emp, salgrade

48. 48 Review Examples from sqlzoo.netsqlzoo.net SELECT L FROM R 1, …, R n WHERE C SELECT L FROM R 1, …, R n WHERE C  L (  C (R 1 x … R n )