Matthew P. Johnson, OCL2, CISDD CUNY, January OCL2 Oracle 10g: SQL & PL/SQL Session #4 Matthew P. Johnson CISDD, CUNY Fall, 2004

Matthew P. Johnson, OCL2, CISDD CUNY, January 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 )

Matthew P. Johnson, OCL2, CISDD CUNY, January Questions from last time Q: What about double quotes? A: Can’t be used in place of single quotes But can be used when Oracle would otherwise misparse your command, e.g.: 1. Names with spaces:  create table bad table name (a int, b int); 2. Reserved words as names:  create table badfieldname(from int, b int);

Matthew P. Johnson, OCL2, CISDD CUNY, January Questions from last time Q: Can an escape char be an escape string? A: No. SQL> select * from newtable where a like '%\%' escape '\'; A B h%i there SQL> select * from newtable where a like '%\%' escape '\\'; select * from newtable where a like '%\%' escape '\\' * ERROR at line 1: ORA-01425: escape character must be character string of length 1 SQL> select * from newtable where a like '%\%' escape '\'; A B h%i there SQL> select * from newtable where a like '%\%' escape '\\'; select * from newtable where a like '%\%' escape '\\' * ERROR at line 1: ORA-01425: escape character must be character string of length 1

Matthew P. Johnson, OCL2, CISDD CUNY, January Case-sensitivity By default, all matches and comparisons are case-sensitive If want case-insensitive, some options: Convert all to upper or lower case:  SQL> select * from emp where upper(ename) like upper('%la%'); Create a function index  Maybe later… Modify the nls_sort setting:  SQL> alter session set nls_sort=binary_ci;  The other values: binary, binary_ai

Matthew P. Johnson, OCL2, CISDD CUNY, January Disambiguation in Oracle SQL Can rename fields by  Select name as n …  Select name n … But not by  Select name=n… Can rename relations only by  … from tab t1, tab t2 Lesson: if you get errors, remove all =s, ASs

Matthew P. Johnson, OCL2, CISDD CUNY, January Disambiguation in Oracle SQL Every selected field must be unambiguous For R(A,B),  Select A from R, R   Select R1.A from R R1, R R2 Consider: Why? * is shorthand for all fields, each must be unambiguous  Select * from R R1, R R2 SQL> Select * from R, R; Select * from R, R * ERROR at line 1: ORA-00918: column ambiguously defined SQL> Select * from R, R; Select * from R, R * ERROR at line 1: ORA-00918: column ambiguously defined

Matthew P. Johnson, OCL2, CISDD CUNY, January SQL e.g. Acc(name,ssn,balance) Q: Who has the largest balance? Conceptually:  name (Acc) -  a2.name (  a2.bal < Acc.bal (Acc x  a2 (Acc))) In SQL?

Matthew P. Johnson, OCL2, CISDD CUNY, January Nulls in SQL If we don’t have a value, can put a NULL Null can mean several things:  Value does not exists  Value exists but is unknown  Value not applicable The schema specifies whether null is allowed for each attribute  not null if not allowed  Otherwise, null is allowed

Matthew P. Johnson, OCL2, CISDD CUNY, January Null Values x = NULL  4*(3-x)/7 = NULL x = NULL  x + 3 – x = NULL x = NULL  3 + (x-x) = NULL x = NULL  x = ‘Joe’ is UNKNOWN In general: no row use null fields appear in the selection test will pass the test Pace Boole, SQL has three boolean values:  FALSE=0  TRUE=1  UNKNOWN=0.5

Matthew P. Johnson, OCL2, CISDD CUNY, January Null values in boolean expressions C1 AND C2= min(C1, C2) C1 OR C2= max(C1, C2) NOT C1= 1 – C1 height > 6 = UNKNOWN  UNKNOWN OR weight > 190 = UNKOWN  (age < 25) AND UNKNOWN = UNKNOWN SELECT * FROM Person WHERE (age < 25) AND (height > 6 OR weight > 190) SELECT * FROM Person WHERE (age < 25) AND (height > 6 OR weight > 190) E.g. age=20 height is NULL weight=180

Matthew P. Johnson, OCL2, CISDD CUNY, January Comparing null and non-nulls Unexpected behavior: Some Persons are not included! The “trichotomy law” does not hold! SELECT * FROM Person WHERE age = 25 SELECT * FROM Person WHERE age = 25

Matthew P. Johnson, OCL2, CISDD CUNY, January Testing for null values Can test for NULL explicitly:  x IS NULL  x IS NOT NULL But:  x=NULL is always null Now it includes all Persons SELECT * FROM Person WHERE age = 25 OR age IS NULL SELECT * FROM Person WHERE age = 25 OR age IS NULL

Matthew P. Johnson, OCL2, CISDD CUNY, January Example with nulls look at emp table  Select names, salaries, commissions, total salaries  What if commission is null?  nvl

Matthew P. Johnson, OCL2, CISDD CUNY, January Evaluation strategies for SQL queries Semantics of a SQL query defined in terms of the following conceptual evaluation strategy:  Compute the cross-product of relation-list in FROM clause  Discard resulting tuples if they fail WHERE clause  Delete attributes that are not in SELECT clause  If DISTINCT is specified, eliminate duplicate rows Often the least efficient way to compute a query! Optimizer finds better ways, but result is the same

Matthew P. Johnson, OCL2, CISDD CUNY, January Case-sensitivity redux By default, all matches and comparisons are case- sensitive If want case-insensitive, some options: Convert all to upper or lower case:  SQL> select * from emp where upper(ename) = upper(‘blake'); Create a function index  Maybe later… Modify the nls_sort setting:  SQL> alter session set nls_sort=binary_ci;  SQL> alter session set nls_comp=ansi;  The other values: binary, binary_ai

Matthew P. Johnson, OCL2, CISDD CUNY, January Subqueries Powerful feature of SQL: one clause can contain other SQL queries!  So can FROM and HAVING clauses Several ways:  Selection  single constant (scalar) in WHERE  Selection  relation in WHERE  Selection  relation in FROM  Etc.

Matthew P. Johnson, OCL2, CISDD CUNY, January Subquery motivation Consider standard multi-table example:  Purchase(prodname, buyerssn, etc.)  Person(name, ssn, etc.)  What did Conrad buy? As usual, need to AND on equality identifying ssn’s row and buyerssn’s row SELECT Purchase.prodname FROM Purchase, Person WHERE buyerssn = ssn AND name = ‘Conrad’

Matthew P. Johnson, OCL2, CISDD CUNY, January Subquery motivation Purchase(prodname, buyerssn, etc.) Person(name, ssn, etc.) What did Conrad buy? Natural intuition: 1.Go find Conrad’s ssn 2.Then find purchases SELECT ssn FROM Person WHERE name = ‘Conrad’ SELECT Purchase.prodname FROM Purchase, Person WHERE buyerssn = Conrad’s-ssn

Matthew P. Johnson, OCL2, CISDD CUNY, January Subqueries Subquery: copy in Conrad’s selection for his ssn: The subquery returns one value, so the = is valid If it returns more (or fewer), we get a run-time error SELECT Purchase.prodname FROM Purchase WHERE buyerssn = (SELECT ssn FROM Person WHERE name = ‘Conrad’) SELECT Purchase.prodname FROM Purchase WHERE buyerssn = (SELECT ssn FROM Person WHERE name = ‘Conrad’)

Matthew P. Johnson, OCL2, CISDD CUNY, January SQL e.g. People(ssn, name, street, city, state)  assume for clarity that cities are unique Q: Who lives on George’s street? Conceptually:  street=s2 AND city=c2 (  p2(s2,c2) (People) x  street,city (  name=‘George’ (People))) In SQL? Another way, conceptually: People   street,city (  name='George’ (People)) In SQL? Later on…

Matthew P. Johnson, OCL2, CISDD CUNY, January Operators on selections Several new operators applied to (unary) selections: 1. EXISTS R 2. s > ALL R 3. s > ANY R > is just an example op Each expression can be negated with NOT

Matthew P. Johnson, OCL2, CISDD CUNY, January Subqueries returning relations Q: Find companies Martha bought from Intuition:  Find Martha’s ssn  Find Martha’s products  Find those products’ companies SELECT Product.maker FROM Product WHERE Product.name IN (SELECT Purchase.product FROM Purchase WHERE Purchase.buyerssn = (SELECT ssn FROM Person WHERE name = ‘Martha’)) SELECT Product.maker FROM Product WHERE Product.name IN (SELECT Purchase.product FROM Purchase WHERE Purchase.buyerssn = (SELECT ssn FROM Person WHERE name = ‘Martha’))

Matthew P. Johnson, OCL2, CISDD CUNY, January Subqueries returning relations Equivalent to: But are they really equivalent? Make both distinct to be sure SELECT Product.maker FROM Product, Purchase, People WHERE Product.name = Purchase.product AND Purchase.buyerssn = ssn AND name = ‘Martha’ SELECT Product.maker FROM Product, Purchase, People WHERE Product.name = Purchase.product AND Purchase.buyerssn = ssn AND name = ‘Martha’

Matthew P. Johnson, OCL2, CISDD CUNY, January Subqueries returning relations SELECT name FROM Product WHERE price > ALL (SELECT price FROM Purchase WHERE maker=‘Gizmo-Works’) SELECT name FROM Product WHERE price > ALL (SELECT price FROM Purchase WHERE maker=‘Gizmo-Works’) Product (pname, price, category, maker) Find products that are more expensive than all Gizmo-Works products You can also use: s > ALL R s > ANY R EXISTS R

Matthew P. Johnson, OCL2, CISDD CUNY, January Correlated Queries So far, subquery executed once;  result used for higher query More complicated: correlated queries “[T]he subquery… [is] evaluated many times, once for each assignment of a value to some term in the subquery that comes from a tuple variable outside the subquery” (Ullman, p286). Q: What does this mean? A: That subqueries refer to vars from outer queries

Matthew P. Johnson, OCL2, CISDD CUNY, January Correlated Queries Movie (title, year, director, length) Q: Find titles that are titles of multiple movies Note (1) scope of variables (2) this can still be expressed as single SFW SELECT DISTINCT title FROM Movie AS x WHERE year <> ANY (SELECT year FROM Movie WHERE title = x.title); SELECT DISTINCT title FROM Movie AS x WHERE year <> ANY (SELECT year FROM Movie WHERE title = x.title); correlation

Matthew P. Johnson, OCL2, CISDD CUNY, January Complex Correlated Query Product (pname, price, category, maker, year) Find products (and their manufacturers) that are more expensive than all products made by the same manufacturer before 1972 Powerful, but much harder to optimize! SELECT DISTINCT pname, maker FROM Product AS x WHERE price > ALL (SELECT price FROM Product AS y WHERE x.maker = y.maker AND y.year < 1972); SELECT DISTINCT pname, maker FROM Product AS x WHERE price > ALL (SELECT price FROM Product AS y WHERE x.maker = y.maker AND y.year < 1972);

Matthew P. Johnson, OCL2, CISDD CUNY, January FROM subqueries Recall Q: Which companies did Martha buy from? Before: found ssn, found products, found companies SELECT Product.maker FROM Product WHERE Product.name IN (SELECT Purchase.product FROM Purchase WHERE Purchase.buyerssn = (SELECT ssn FROM Person WHERE name = ‘Martha’)) SELECT Product.maker FROM Product WHERE Product.name IN (SELECT Purchase.product FROM Purchase WHERE Purchase.buyerssn = (SELECT ssn FROM Person WHERE name = ‘Martha’))

Matthew P. Johnson, OCL2, CISDD CUNY, January FROM subqueries Motivation for another way: suppose we’re given Martha’s purchases Then could just cross with Products and select identified rows  Substitute (named) subquery for Martha’s purchases SELECT Product.maker FROM Product, (SELECT Purchase.product FROM Purchase WHERE Purchase.buyerssn = (SELECT ssn FROM Person WHERE name = ‘Martha’)) Marthas WHERE Product.name = Martha.product SELECT Product.maker FROM Product, (SELECT Purchase.product FROM Purchase WHERE Purchase.buyerssn = (SELECT ssn FROM Person WHERE name = ‘Martha’)) Marthas WHERE Product.name = Martha.product

Matthew P. Johnson, OCL2, CISDD CUNY, January Existential/Universal Conditions Product (pname, price, company) Company(cname, city) Find all companies s.t. some of their products have price < 100 SELECT DISTINCT Company.cname FROM Company, Product WHERE Company.cname = Product.company and Produc.price < 100 SELECT DISTINCT Company.cname FROM Company, Product WHERE Company.cname = Product.company and Produc.price < 100 Existential: easy!

Matthew P. Johnson, OCL2, CISDD CUNY, January Existential/Universal Conditions Product (pname, price, company) Company(cname, city) Find all companies s.t. all of their products have price < 100 Universal: hard!

Matthew P. Johnson, OCL2, CISDD CUNY, January Existential/universal with IN 2. Find all companies s.t. all their products have price < Find the other companies: i.e. s.t. some product  100 SELECT DISTINCT Company.cname FROM Company WHERE Company.cname IN (SELECT Product.company FROM Product WHERE Produc.price >= 100 SELECT DISTINCT Company.cname FROM Company WHERE Company.cname IN (SELECT Product.company FROM Product WHERE Produc.price >= 100 SELECT DISTINCT Company.cname FROM Company WHERE Company.cname NOT IN (SELECT Product.company FROM Product WHERE Produc.price >= 100 SELECT DISTINCT Company.cname FROM Company WHERE Company.cname NOT IN (SELECT Product.company FROM Product WHERE Produc.price >= 100

Matthew P. Johnson, OCL2, CISDD CUNY, January More on Set-Comparison Operators We’ve already seen IN R, NOT IN R. Can also use EXISTS R, NOT EXISTS R Also available: op ANY R, op ALL R Find sailors whose rating is greater than that of some sailor called Alberto: SELECT R.SID FROM Reserves R WHERE R.rating > ANY ( SELECT R2.rating FROM Reserves R2 WHERE R2.sname=‘Alberto’)

Matthew P. Johnson, OCL2, CISDD CUNY, January Joins operations Variations:  Cross join (Cartesian product)  Join … On  Natural join  Outer join Apply to relations appearing in selections

Matthew P. Johnson, OCL2, CISDD CUNY, January Cross join - example 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

Matthew P. Johnson, OCL2, CISDD CUNY, January Cross join – example Select * From MovieStar Cross Join MovieExec 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

Matthew P. Johnson, OCL2, CISDD CUNY, January Join … On: example Select * From MovieStar Join MovieExec On MovieStar.Name <> MovieExec. Name MovieSt ar.name MovieStar.addr ess MovieSta r. Gender MovieStar. Birthdate MovieExe c. Name MovieExec.Add ress MovieEx ec. Networth Hanks123 Palm RdM01/01/60Spielber g 246 Palm Rd10M Hanks123 Palm RdM01/01/60Taylor456 Maple Av20M Hanks123 Palm RdM01/01/60Lucas789 Oak St30M Taylor456 Maple AvF02/02/40Spielber g 246 Palm Rd10M Taylor456 Maple AvF02/02/40Taylor456 Maple Av20M Taylor456 Maple AvF02/02/40Lucas789 Oak St30M Lucas789 Oak StM03/03/55Spielber g 246 Palm Rd10M Lucas789 Oak StM03/03/55Taylor456 Maple Av20M Lucas789 Oak StM03/03/55Lucas789 Oak St30M Row

Matthew P. Johnson, OCL2, CISDD CUNY, January Natural Joins MovieStar(name, address, gender, birthdate) MovieExec(name, address, networth) Natural Join: MovieStar Natural Join MovieExec; Results in: list of individuals who are movie- stars as well as executives: (Name, address, gender, birthdate, networth)

Matthew P. Johnson, OCL2, CISDD CUNY, January Example - Natural join NameAddressGenderBirthdate Hanks123 Palm RdM01/01/60 Taylor456 Maple AvF02/02/40 Lucas789 Oak StM03/03/55 NameAddressNetworth Spielberg246 Palm Rd10M Taylor456 Maple Av 20M Lucas789 Oak St30M MovieStar MovieExec NameAddressGenderBirthdateNetworth Taylor456 Maple AvF02/02/4020M Lucas789 Oak StM03/03/5530M Select *from MovieStar Natural Join MovieExec

Matthew P. Johnson, OCL2, CISDD CUNY, January Outer Join - Example 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 NameAddressGenderBirthdateNetworth Hanks123 Palm RdM01/01/60NULL Spielberg246 Palm RdNULL 10M Taylor456 Maple AvF02/02/4020M Lucas789 Oak StM03/03/5530M MovieStarMovieExec Select *from MovieStar FULL OUTER JOIN MovieExec on MovieStart.name=MovieExec.name

Matthew P. Johnson, OCL2, CISDD CUNY, January Outer Join - Example Select * from MovieStar LEFT OUTER JOIN MovieExec on MovieStart.name=MovieExec.name NameAddressGenderBirthdateNetworth Hanks123 Palm RdM01/01/60NULL Spielberg246 Palm RdNULL 10M Taylor456 Maple AvF02/02/4020M Lucas789 Oak StM03/03/5530M Select *from MovieStar RIGHT OUTER JOIN MovieExec on MovieStart.name=MovieExec.name NameAddressGenderBirthdateNetworth Hanks123 Palm RdM01/01/60NULL Spielberg246 Palm RdNULL 10M Taylor456 Maple AvF02/02/4020M Lucas789 Oak StM03/03/5530M

Matthew P. Johnson, OCL2, CISDD CUNY, January New-style join syntax Old-style syntax simply lists tables separated by commas:  SELECT * FROM A, B WHERE …; New-style makes the join explicit:  SELECT * FROM A JOIN B ON … WHERE …

Matthew P. Johnson, OCL2, CISDD CUNY, January New-style join syntax Functionally equivalent to old-style, but perhaps more elegant Introduced in Oracle 8i Older versions / other DBMSs may only support old-style syntax

Matthew P. Johnson, OCL2, CISDD CUNY, January 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

Matthew P. Johnson, OCL2, CISDD CUNY, January New-style outer joins Outer joins may be left, right, or middle  FROM A LEFT [OUTER] JOIN B;  FROM A RIGHT [OUTER] JOIN B;  FROM A FULL [OUTER] JOIN B; “OUTER” is optional If “OUTER” is included, then “FULL” is the default Q: How to remember left v. right? A: It indicates the side whose rows are always included

Matthew P. Johnson, OCL2, CISDD CUNY, January Old-style outer joins Outer joins can also be done with the old-style syntax, but with the (+) …WHERE A.att=B.att(+) corresponds to: …FROM A LEFT JOIN B; The (+) is applied to all B attributes referred to in the WHERE clause Q: How to remember which side gets the (+)? A: The side that gets null rows “added”

Matthew P. Johnson, OCL2, CISDD CUNY, January SQL e.g. People(ssn, name, street, city, state)  assume for clarity that cities are unique Q: Who lives on George’s street? Now, the second way, conceptually: People   street,city (  name=“George” (People)) In SQL?

Matthew P. Johnson, OCL2, CISDD CUNY, January Live Examples Examples from sqlzoo.netsqlzoo.net