1. M.P. Johnson, DBMS, Stern/NYU, Sp20041 C20.0046: Database Management Systems Lecture #10 Matthew P. Johnson Stern School of Business, NYU Spring, 2004

2. M.P. Johnson, DBMS, Stern/NYU, Sp2004 2 Agenda Last time: R.A., Bags This time: 1. Finish R.A. 2. Begin SQL Project Part 2 due now Something else assigned soon

3. M.P. Johnson, DBMS, Stern/NYU, Sp2004 3 Relational Algebra Review Five basic operators:  Union:  Intersection: Difference: -  Selection:   Projection:   Cartesian Product:  Extended operators:  Joins (equijoin, theta join, semijoin, outerjoin)  Renaming:   Extended projection   Sorting   Grouping-and-aggregation op 

4. M.P. Johnson, DBMS, Stern/NYU, Sp2004 4 Sorting So far, everything’s an unordered bag But sometimes order is nice Sort op  L (R) produces a list, not a bag No operators operate on lists   if sort called, generally last op Subscript L = a 1,a 2,… in op is the list of attributes to sort on  Rows sorted by attributes  Rows with same a 1 value sorted by a 2, etc.

5. M.P. Johnson, DBMS, Stern/NYU, Sp2004 5 Outerjoin Like L ⋈ R except that dangling tuples are included, padded with nulls Left outerjoin: dangling tuples from L are include  Nulls appear “on the right” Right outerjoin: dangling tuples from R are included  Nulls appear “on the left”

6. M.P. Johnson, DBMS, Stern/NYU, Sp2004 6 Constraints on Relations (5.5) Ref. integ., FDs, other constraints are expressible in RA Two basic tools: 1. R =   Assert R is empty 2. R  S  Assert R is a subset of S NB: They’re equivalent R  S iff R – S =  R =  iff R  S-S (for arbitrary S)

7. M.P. Johnson, DBMS, Stern/NYU, Sp2004 7 Expressing referential integrity Relations:  Reps(ssn, name, etc.)  Clients(ssn, name, rssn) Suppose we require: each client gets a sales rep a client’s row contains an rssn  must have a rep with that ssn How to require this in RA? Every Clients.rssn must be in the set of Reps.ssns  rssn (Clients)   ssn (Reps) Or:  rssn (Clients) –  ssn (Reps) = 

8. M.P. Johnson, DBMS, Stern/NYU, Sp2004 8 Expressing referential integrity Also works for multiple attributes Relations: StarsIn(SName,Title,Year) Movies(Title, Year, Length, Studio) Require: every movie referenced by StarsIn to exist Write:  Title,Year (StarsIn)   Title,Year (Movies)

9. M.P. Johnson, DBMS, Stern/NYU, Sp2004 9 Expressing FDs Relation: Employees(name,ssn,address,gender, etc.) Has FD: ssn  address What does the FD mean? No matter how we choose two rows, if they agree on ssn, then they agree on address So, strategy: choose pairs all possible ways; Select pairs that agree on ssn but not address; Check how many we get First, rename one copy to E1 and one to E2   E1 (Employees),  E2 (Employees) Then:  E1.ssn=E2.ssn AND E1.address != E2.address (E1 x E2) = 

10. M.P. Johnson, DBMS, Stern/NYU, Sp2004 10 Expressing domain constraints Constraint on legal values for attributes Employees(name,ssn,address,gender etc.) Gender should be M/F Select bad ones and check count  gender!=‘F’ AND gender!=‘M’ (Employees) = 

11. M.P. Johnson, DBMS, Stern/NYU, Sp2004 11 Expressing other constraints Relations: MovieExecs(name, address, ssn, netWorth) Studios(name, address, presSsn) Constraint: Studio presidents must be worth at leat $10,000,000 First, theta-join presSsn to ssn, then select ones w/ < $10M, then check count:  netWorth<10000000 (Studio ⋈ presSsn=ssn MEs) =  Or: Select MEs w/ >= $10M, then check that they contain all studio presidents:  presSsn (Studios)  ssn (  netWorth<10000000 (MEs))

12. M.P. Johnson, DBMS, Stern/NYU, Sp2004 12 Recap: You are here First part of course is done: conceptual foundations You now know:  E/R Model  Relational Model  Relational Algebra 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  Express queries in relational algebra Next:  Create, update, query SQL tables  Write SQL/DB-connected applications

13. M.P. Johnson, DBMS, Stern/NYU, Sp2004 13 Next topic: SQL (6.1) Standard language for querying and manipulating data Structured Query Language Many standards: ANSI SQL, SQL92/SQL2, SQL3/SQL99 Vendors support various subsets/extensions We’ll do SQL99/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)

14. M.P. Johnson, DBMS, Stern/NYU, Sp2004 14 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

15. M.P. Johnson, DBMS, Stern/NYU, Sp2004 15 “Tables” PNamePriceCategoryManufacturer Gizmo$19.99GadgetsGizmoWorks Powergizmo$29.99GadgetsGizmoWorks SingleTouch$149.99PhotographyCanon MultiTouch$203.99HouseholdHitachi Product Attribute names Table name Tuples or rows

16. M.P. Johnson, DBMS, Stern/NYU, Sp2004 16 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”

17. M.P. Johnson, DBMS, Stern/NYU, Sp2004 17 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”

18. M.P. Johnson, DBMS, Stern/NYU, Sp2004 18 A Notation for SQL Queries SELECT Name, Price, Manufacturer FROM Product WHERE Price > 100 Product(PName, Price, Category, Manfacturer) Answer(PName, Price, Manfacturer) Input Schema Output Schema

19. M.P. Johnson, DBMS, Stern/NYU, Sp2004 19 R.A.  SQL R.A. Projection   SQL SELECT R.A. Selection   SQL WHERE R.A. Join  SQL FROM  Comma-separated list… What goes in the WHERE clause: x = y, x < y, x <= y, etc.  For number, they have the usual meanings  For CHAR and VARCHAR: lexicographic ordering Expected conversion between CHAR and VARCHAR  For dates and times, what you expect

20. M.P. Johnson, DBMS, Stern/NYU, Sp2004 20 R.A.  SQL Movies(Title,Year,Length,inColor,Studio,Prdcr#) Q: How long was Star Wars (1977), in R.A.? Q: In SQL? Q: Which Fox movies are are at least 100 minutes long, in R.A.? Q: In SQL?

21. M.P. Johnson, DBMS, Stern/NYU, Sp2004 21 R.A.  SQL Reps(ssn, name, etc.) Clients(ssn, name, rssn) Q: Who are George’s clients, in R.A.? Second answer from last time:   Clients.name (  Reps.name=“George” and Reps.ssn=rssn (Reps x Clients)) In SQL?

22. M.P. Johnson, DBMS, Stern/NYU, Sp2004 22 The LIKE operator s LIKE p: pattern matching on strings p may contain two special symbols:  _ = any single character  % = zero or more chars Product(Name, Price, Category, Manufacturer) Find all products whose name contains ‘gizmo’: SELECT * FROM Products WHERE PName LIKE ‘%gizmo%’

23. M.P. Johnson, DBMS, Stern/NYU, Sp2004 23 The LIKE operator Q: What it want to search for values containing a ‘%’? PName LIKE ‘%%’ won’t work Instead, must use escape chars In C/C++/J, prepend ‘\’ In SQL, prepend an arbitrary escape char: PName LIKE ‘x%x%’ ESCAPE ‘x’

24. M.P. Johnson, DBMS, Stern/NYU, Sp2004 24 Eliminating Duplicates SELECT DISTINCT category FROM Product SELECT DISTINCT category FROM Product Compare to: SELECT category FROM Product SELECT category FROM Product Category Gadgets Photography Household Category Gadgets Photography Household

25. M.P. Johnson, DBMS, Stern/NYU, Sp2004 25 Ordering the Results Ordering is ascending, unless you specify the DESC keyword per attribute. SELECT pname, price, manufacturer FROM Product WHERE category=‘gizmo’ AND price > 50 ORDER BY price, pname SELECT pname, price, manufacturer FROM Product WHERE category=‘gizmo’ AND price > 50 ORDER BY price, pname SELECT pname, price, manufacturer FROM Product WHERE category=‘gizmo’ AND price > 50 ORDER BY price DESC, pname ASC SELECT pname, price, manufacturer FROM Product WHERE category=‘gizmo’ AND price > 50 ORDER BY price DESC, pname ASC

26. M.P. Johnson, DBMS, Stern/NYU, Sp2004 26 Ordering the Results SELECTCategory FROMProduct ORDER BYPName SELECTCategory FROMProduct ORDER BYPName PNamePriceCategoryManufacturer Gizmo$19.99GadgetsGizmoWorks Powergizmo$29.99GadgetsGizmoWorks SingleTouch$149.99PhotographyCanon MultiTouch$203.99HouseholdHitachi ?

27. M.P. Johnson, DBMS, Stern/NYU, Sp2004 27 Ordering the Results SELECT DISTINCT category FROMProduct ORDER BYcategory SELECT DISTINCT category FROMProduct ORDER BYcategory Compare to: Category Gadgets Household Photography SELECT DISTINCT category FROMProduct ORDER BYPName SELECT DISTINCT category FROMProduct ORDER BYPName ?

28. M.P. Johnson, DBMS, Stern/NYU, Sp2004 28 Joins in SQL (6.2) 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?

29. M.P. Johnson, DBMS, Stern/NYU, Sp2004 29 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

30. M.P. Johnson, DBMS, Stern/NYU, Sp2004 30 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

31. M.P. Johnson, DBMS, Stern/NYU, Sp2004 31 Joins in SQL Product (pname, price, category, manufacturer) Company (cname, stockPrice, country) Find all countries that manufacture some product in the ‘Gadgets’ category. SELECTCountry FROMProduct, Company WHEREManufacturer=CName AND Category=‘Gadgets’

32. M.P. Johnson, DBMS, Stern/NYU, Sp2004 32 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’

33. M.P. Johnson, DBMS, Stern/NYU, Sp2004 33 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’

34. M.P. Johnson, DBMS, Stern/NYU, Sp2004 34 Disambiguating Attributes Sometimes two relations have the same attr: Person(pname, address, worksfor) Company(cname, address) SELECT DISTINCT pname, address FROM Person, Company WHERE worksfor = cname SELECT DISTINCT Person.pname, Company.address FROM Person, Company WHERE Person.worksfor = Company.cname Which address ?

35. M.P. Johnson, DBMS, Stern/NYU, Sp2004 35 Tuple Variables SELECT DISTINCT x.store FROM Purchase AS x, Purchase AS y WHERE x.product = y.product AND y.store = ‘BestBuy’ SELECT DISTINCT x.store FROM Purchase AS x, Purchase AS y WHERE x.product = y.product AND y.store = ‘BestBuy’ Find all stores that sold at least one product that the store ‘BestBuy’ also sold: Answer (store) Product (pname, price, category, manufacturer) Purchase (buyer, seller, store, product) Person(persname, phoneNumber, city)

36. M.P. Johnson, DBMS, Stern/NYU, Sp2004 36 Tuple Variables Tuple variables introduced automatically: Product ( name, price, category, manufacturer) Becomes: Doesn’t work when Product occurs more than once In that case the user needs to define variables explicitly SELECT name FROM Product WHERE price > 100 SELECT name FROM Product WHERE price > 100 SELECT Product.name FROM Product AS Product WHERE Product.price > 100 SELECT Product.name FROM Product AS Product WHERE Product.price > 100

37. M.P. Johnson, DBMS, Stern/NYU, Sp2004 37 SQL Query Semantics SELECT a1, a2, …, ak FROM R1 AS x1, R2 AS x2, …, Rn AS xn WHERE Conditions 1. 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

38. M.P. Johnson, DBMS, Stern/NYU, Sp2004 38 SQL Query Semantics SELECT a1, a2, …, ak FROM R1 AS x1, R2 AS x2, …, Rn AS xn WHERE Conditions 2. Parallel assignment 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

39. M.P. Johnson, DBMS, Stern/NYU, Sp2004 39 First Unintuitive SQLism SELECTR.A FROMR, S, T WHERER.A=S.A OR R.A=T.A Looking for R  (S  T) But what happens if T is empty? See transcript of this in Oracle on salestranscript