SQL. Ilchul Yoon Assistant Professor State University of New York, Korea. on tables. describing schema. CSE 532 Theory of Database Systems

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1 CSE 532 Theory of Database Systems Lecture 03 SQL Ichu Yoon Assistant Professor State University of New York, Korea Adapted from book authors sides SQL Language for describing database schema & operations on tabes Data Definition Language (DDL): subanguage of SQL for describing schema 2 1

sides SQL Language for describing database schema & operations on tabes

2 Tabes SQL entity that corresponds to a reation An eement of the database schema 3 Tabe Decaration CREATE TABLE Student ( Id: INTEGER, Name: CHAR(20), Address: CHAR(50), Status: CHAR(10) ) Id Name Address Status John 10 Cedar St Freshman Mary 22 Main St Sophomore Student 4 2

CHAR(20), Address: CHAR(50), Status: CHAR(10) ) Id Name Address Status

3 Primary/Candidate Keys CREATE TABLE Course ( CrsCode CHAR(6), CrsName CHAR(20), DeptId CHAR(4), Descr CHAR(100), PRIMARY KEY (CrsCode), UNIQUE (DeptId, CrsName) -- candidate key ) Comments start with 2 dashes 5 Nu Probem: Not a information might be known when row is inserted (e.g., Grade might be missing from Transcript) A coumn might not be appicabe for a particuar row (e.g., MaidenName if row describes a mae) Soution: Use pace hoder nu Not a vaue of any domain (athough caed nu vaue) Indicates the absence of a vaue Not aowed in certain situations Primary keys and coumns constrained by NOT NULL 6 3

4 Defaut Vaue Vaue to be assigned if attribute vaue in a row is not specified CREATE TABLE Student ( Id INTEGER, Name CHAR(20) NOT NULL, Address CHAR(50), Status CHAR(10) DEFAULT freshman, PRIMARY KEY (Id) ) 7 Semantic Constraints in SQL Primary key and foreign key are eampes of structura constraints Semantic constraints Epress the ogic of the appication at hand: e.g., number of registered students maimum enroment 8 4

7 Semantic Constraints in SQL Primary key and foreign key are eampes of structura constraints Semantic

5 Semantic Constraints (cont d) Used for appication dependent conditions Eampe: imit attribute vaues CREATE TABLE Transcript ( StudId INTEGER, CrsCode CHAR(6), Semester CHAR(6), Grade CHAR(1), CHECK (Grade IN ( A, B, C, D, F )), CHECK (StudId > 0 AND StudId < ) ) Each row in tabe must satisfy condition 9 Semantic Constraints (cont d) Eampe: reate vaues of attributes in different coumns CREATE TABLE Empoyee ( Id INTEGER, Name CHAR(20), Saary INTEGER, MngrSaary INTEGER, CHECK ( MngrSaary > Saary) ) 10 5

StudId < 1000000000) ) Each row in tabe must satisfy condition 9 Semantic Constraints (cont d) Eampe: reate vaues of attributes

6 Constraints Probems Probem 1: Empty tabe aways satisfies a CHECK constraints (an idiosyncrasy of the SQL standard) CREATE TABLE Empoyee ( Id INTEGER, Name CHAR(20), Saary INTEGER, MngrSaary INTEGER, CHECK ( 0 < (SELECT COUNT (*) FROM Empoyee)) ) If Empoyee is empty, there are no rows on which to evauate the CHECK condition. 11 Constraints Probems Probem 2: Inter-reationa constraints shoud be symmetric CREATE TABLE Empoyee ( Id INTEGER, Name CHAR(20), Saary INTEGER, MngrSaary INTEGER, CHECK ((SELECT COUNT (*) FROM Manager) < (SELECT COUNT (*) FROM Empoyee)) ) Why shoud constraint be in Empoyee and not Manager? What if Empoyee is empty? 12 6

7 Assertion Eement of schema (ike tabe) Symmetricay specifies an inter-reationa constraint Appies to entire database (not just the individua rows of a singe tabe) Does it work even if Empoyee is empty? CREATE ASSERTION DontFireEveryone CHECK (0 < SELECT COUNT (*) FROM Empoyee) 13 Assertion CREATE ASSERTION KeepEmpoyeeSaariesDown CHECK (NOT EXISTS( SELECT * FROM Empoyee E WHERE E.Saary > E.MngrSaary)) 14 7

CREATE ASSERTION DontFireEveryone CHECK (0 < SELECT COUNT (*) FROM Empoyee) 13 Assertion CREATE

8 Assertions and Incusion Dependency Courses with no students CREATE ASSERTION NoEmptyCourses CHECK (NOT EXISTS ( SELECT * FROM Teaching T WHERE -- for each row T check -- the foowing condition NOT EXISTS ( SELECT * FROM Transcript R WHERE T.CrsCode = R.CrsCode AND T.Semester = R.Semester) ) ) Students in a particuar course 15 Domains Possibe attribute vaues can be specified Using a CHECK constraint or Creating a new domain Domain can be used in severa decarations Domain is a schema eement CREATE DOMAIN Grades CHAR (1) CHECK (VALUE IN ( A, B, C, D, F )) CREATE TABLE Transcript (., Grade: Grades, ) 16 8

Semester) ) ) Students in a particuar course 15 Domains Possibe attribute vaues can be specified Using a CHECK constraint or Creating a new domain

9 Foreign Key Constraint CREATE TABLE Teaching ( ProfId INTEGER, CrsCode CHAR (6), Semester CHAR (6), PRIMARY KEY (CrsCode, Semester), FOREIGN KEY (CrsCode) REFERENCES Course, FOREIGN KEY (ProfId) REFERENCES Professor (Id) ) 17 Foreign Key Constraint CrsCode CrsCode ProfId y Course Teaching Id y Professor 18 9

(CrsCode) REFERENCES Course, FOREIGN KEY (ProfId) REFERENCES Professor (Id) )

10 Circuarity in Foreign Key Constraint A 1 A 2 A 3 B 1 B 2 B 3 A y y B candidate key: A 1 foreign key: A 3 references B(B 1 ) candidate key: B 1 foreign key: B 3 references A(A 1 ) Probem 1: Creation of A requires eistence of B and vice versa Soution: CREATE TABLE A ( ) -- no foreign key CREATE TABLE B ( ) -- incude foreign key ALTER TABLE A ADD CONSTRAINT cons FOREIGN KEY (A 3 ) REFERENCES B (B 1 ) 19 Circuarity in Foreign Key Constraint (cont d) Probem 2: Insertion of row in A requires prior eistence of row in B and vice versa Soution: use appropriate constraint checking mode: IMMEDIATE checking DEFERRED checking 20 10

incude foreign key ALTER TABLE A ADD CONSTRAINT cons FOREIGN KEY (A 3 ) REFERENCES B (B 1 ) 19 Circuarity in Foreign Key Constraint (cont d) Probem 2:

11 Reactive Constraints Constraints enabe DBMS to recognize a bad state and reject the statement or transaction that creates it More generay, it woud be nice to have a mechanism that aows a user to specify how to react to a vioation of a constraint SQL-92 provides a imited form of such a reactive mechanism for foreign key vioations 21 Handing Foreign Key Vioations Insertion into A: Reject if no row eists in B containing foreign key of inserted row Deetion from B: NO ACTION: Reject if row(s) in A references row to be deeted (defaut response) A? B Request to deete row rejected 22 11

reactive mechanism for foreign key vioations 21 Handing Foreign Key Vioations Insertion into A: Reject if no row eists in B containing foreign

12 Handing Foreign Key Vioations (cont d) Deetion from B (cont d): SET NULL: Set vaue of foreign key in referencing row(s) in A to nu A nu B Row deeted 23 Handing Foreign Key Vioations (cont d) Deetion from B (cont d): SET DEFAULT: Set vaue of foreign key in referencing row(s) in A to defaut vaue (y) which must eist in B A y y B Row deeted 24 12

Vioations (cont d) Deetion from B (cont d): SET DEFAULT: Set vaue of foreign key in

13 Handing Foreign Key Vioations (cont d) Deetion from B (cont d): CASCADE: Deete referencing row(s) in A as we A B 25 Handing Foreign Key Vioations (cont d) Update (change) foreign key in A: Reject if no row eists in B containing new foreign key Update candidate key in B (to z) same actions as with deetion: NO ACTION: Reject if row(s) in A references row to be updated (defaut response) SET NULL: Set vaue of foreign key to nu SET DEFAULT: Set vaue of foreign key to defaut CASCADE: Propagate z to foreign key Cascading when key in B changed from to z A z z B 26 13

same actions as with deetion: NO ACTION: Reject if row(s) in A references row to be updated (defaut response) SET NULL: Set vaue of foreign

14 Handing Foreign Key Vioations (cont d) The action taken to repair the vioation of a foreign key constraint in A may cause a vioation of a foreign key constraint in C The action specified in C contros how that vioation is handed; If the entire chain of vioations cannot be resoved, the initia deetion from B is rejected. y y C A B 27 Specifying Actions CREATE TABLE Teaching ( ProfId INTEGER, CrsCode CHAR (6), Semester CHAR (6), PRIMARY KEY (CrsCode, Semester), FOREIGN KEY (ProfId) REFERENCES Professor (Id) ON DELETE NO ACTION ON UPDATE CASCADE, FOREIGN KEY (CrsCode) REFERENCES Course (CrsCode) ON DELETE SET NULL ON UPDATE CASCADE ) 28 14

y y C A B 27 Specifying Actions CREATE TABLE Teaching ( ProfId INTEGER, CrsCode CHAR (6), Semester CHAR (6), PRIMARY KEY (CrsCode, Semester), FOREIGN KEY

15 Triggers A more genera mechanism for handing events Not in SQL-92, but is in SQL:1999 Trigger is a schema eement (ike tabe, assertion, ) CREATE TRIGGER CrsChange AFTER UPDATE OF CrsCode, Semester ON Transcript WHEN (Grade IS NOT NULL) ROLLBACK Guard 29 Views Schema eement Part of eterna schema A virtua tabe constructed from actua tabes on the fy Can be accessed in queries ike any other tabe Not materiaized, constructed when accessed 30 15

(Grade IS NOT NULL) ROLLBACK Guard 29 Views Schema eement Part of eterna schema A virtua tabe constructed from

16 Views - Eampes Part of eterna schema suitabe for use in Bursar s office: CREATE VIEW CoursesTaken (StudId, CrsCode, Semester) AS SELECT T.StudId, T.CrsCode, T.Semester FROM Transcript T Part of eterna schema suitabe for student with Id : CREATE VIEW CoursesITook (CrsCode, Semester, Grade) AS SELECT T.CrsCode, T.Semester, T.Grade FROM Transcript T WHERE T.StudId = Modifying the Schema ALTER TABLE Student ADD COLUMN Gpa INTEGER DEFAULT 0 ALTER TABLE Student ADD CONSTRAINT GpaRange CHECK (Gpa >= 0 AND Gpa <= 4) ALTER TABLE Transcript DROP CONSTRAINT Cons -- constraint names are usefu DROP TABLE Empoyee DROP ASSERTION DontFireEveryone 32 16

Semester, T.Grade FROM Transcript T WHERE T.

17 Constraint Name Eampe CREATE TABLE TRANSCRIPT ( StudID INTEGER, CrsCode CHAR(6), Semester CHAR(6), Grade GRADES, CONSTRAINT TRKEY PK (Sid, C, Sem) CONSTRAINT STUDFK FK (Sid) REFERENCES STUDENT, CONSTRAINT CRSFK FK (C) REFERENCES COURSE, CONSTRAINT IDRANGE CHECK ( Sid > 0 AND Sid < ) ) ALTER TABLE TRANSCRIPT DROP CONSTRAINT STUDFK 33 Access Contro Databases might contain sensitive information Access has to be imited: Users have to be identified authentication Generay done with passwords Each user must be imited to modes of access appropriate to that user - authorization SQL:92 provides toos for specifying an authorization poicy but does not support authentication (vendor specific) 34 17

Contro Databases might contain sensitive information Access has to be imited: Users have to be identified authentication Generay done with passwords Each user must be imited

18 Controing Authorization in SQL GRANT access_ist ON tabe TO user_ist [WITH GRANT OPTION] Access modes: SELECT, INSERT, DELETE, UPDATE, REFERENCES GRANT UPDATE (Grade) ON Transcript TO prof_smith Ony the Grade coumn can be updated by prof_smith GRANT SELECT ON Transcript TO joe Individua coumns cannot be specified for SELECT access (in the SQL standard) a coumns of Transcript can be read But SELECT access contro to individua coumns can be simuated through views (net) 35 Controing Authorization in SQL Using Views GRANT SELECT ON CoursesTaken TO joe GRANT access ON view TO user_ist Thus views can be used to simuate access contro to individua coumns of a tabe 36 18

(in the SQL standard) a coumns of Transcript can be read But SELECT access contro to individua coumns can be simuated through views (net) 35 Controing Authorization

19 Authorization Mode REFERENCES Foreign key constraint enforces reationship between tabes that can be epoited to Contro access: can enabe perpetrator prevent deetion of rows CREATE TABLE DontDismissMe ( Id INTEGER, FOREIGN KEY (Id) REFERENCES Student ON DELETE NO ACTION ) GRANT REFERENCES ON Student TO Joe Revea information: successfu insertion into DontDissmissMe means a row with foreign key vaue eists in Student INSERT INTO DontDismissMe ( ) 37 19

(Id) REFERENCES Student ON DELETE NO ACTION ) GRANT REFERENCES ON Student TO Joe Revea information: successfu

Database Design. Goal: specification of database schema Methodology: E-R Model is viewed as a set of

Database Design. Goal: specification of database schema Methodology: E-R Model is viewed as a set of Database Design Goal: specification of database schema Methodology: Use E-R model to get a high-level graphical view of essential components of the model and how they are related Convert E-R diagram to