1. Chapter 8 Part 1 SQL-99 Schema Definition, Constraints, Queries, and Views

2. 2 Chapter Outline SQL Data Definition and Data Type  Schema and catalog concepts in SQL  The CREATE TABLE command in SQL  Attribute data types and domains in SQL Specifying Constraints in SQL  Specifying attribute constraints and attribute defaults  Specifying key and referential integrity constraints  Giving names to constraints  Specifying constraints on tuples using CHECK Schema Change Statements in SQL  The DROP command  The ALTER command Basic Queries in SQL

3. 3 Database Design Steps in building a database for an application: Real-world domain Conceptual model DBMS data model Create Schema (DDL) Load data (DML)

4. 4 Introduction SQL (Structured Query Language) SQL was called SEQUEL (Structured English QUEry Language) was designed and implemented by IBM SQL is now the stander language for commercial relational DBMSs. SQL was standardized first by the ANSI and ISO. called SQL1 or SQL-86 Much expanded standard called SQL2 or SQL-92 The next standard that is well-recognized is SQL-99 or SQL3

5. 5 DDL Statements The main SQL data definition language statements are: Used to CREATE, DROP, and ALTER the descriptions of the tables (relations) of a database CREATE DOMAIN ALTER DOMAINDROP DOMAIN CREATE TABLE ALTER TABLEDROP TABLE CREATE VIEW DROP VIEW CREATE INDEXDROP INDEX

6. 6 Specifies a new base relation by giving it a name, and specifying each of its attributes and their data types (INTEGER, FLOAT, DECIMAL(i,j), CHAR(n), VARCHAR(n)) A constraint NOT NULL may be specified on an attribute CREATE TABLE DEPARTMENT ( DnameVARCHAR(10)NOT NULL, DnumberINTEGERNOT NULL, Mgr_ssnCHAR(9), Mgr_start_dateCHAR(9) ); SQL Data Definition and Data Type: The CREATE TABLE command in SQL

7. 7 CREATE TABLE (contd.) In SQL2, can use the CREATE TABLE command for specifying the primary key attributes, secondary keys, and referential integrity constraints (foreign keys). Key attributes can be specified via the PRIMARY KEY and UNIQUE phrases CREATE TABLE DEPARTMENT ( DnameVARCHAR(10)NOT NULL, DnumberINTEGERNOT NULL, Mgr_ssnCHAR(9), Mgr_start_dateCHAR(9), PRIMARY KEY (Dnumber), UNIQUE (Dname), FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE (Ssn));

8. 8 Identifiers Names May contain A-Z, a-z, 0-9, _ No longer than 128 characters Start with letter Cannot contain spaces

9. 9 SQL Data Definition and Data Type: Attribute data types and domains in SQL Type SQL Data Type Used Numeric INTEGER or INT and SMALLINT Integer numbers of various sizes FLOAT or REAL and DOUBLE PRECISION Floating-point (real) numbers of various precision NUMERIC (i, j) or DECIMAL (i, j) Formatted numbers, where i The precision and j the scale Character- string CHAR(n) or CHARACTER(n) Fixed length, where n is the number of characters VARCHAR(n) or CHAR VARYING(n) or CHARACTER VARYING(n) Varying length, where n is the maximum number of characters

10. 10 SQL Data Definition and Data Type: Attribute data types and domains in SQL (contd.) Type SQL Data Type Used Bit-string BIT(n) Fixed length, where n is the number of bits BIT VARYING (n) Varying length, where n is the maximum number of bits Boolean BOOLEAN There are three values (TRUE,FALSE and UNKNOWN)

11. 11 SQL Data Definition and Data Type: Attribute data types and domains in SQL (contd.) Type SQL Data Type Used Date_Time DATE Has ten positions. Made up of year- month-day in the format yyyy-mm-dd TIME Made up of hour:minute:second in the format hh:mm:ss TIME(i) Made up of hour:minute:second plus i additional digits specifying fractions of a second. format is hh:mm:ss:i Timestamp TIMESTAMP Has both DATE and TIME components INTERVAL Specifies a relative value rather than an absolute value. Can be DAY/TIME intervals or YEAR/MONTH intervals

12. 12 “COMPANY” Relational Database Schema

13. 13 SQL Create Table data definition statements for defining the COMPANY Schema

14. 14 SQL Create Table data definition statements for defining the COMPANY Schema (contd.)

15. 15 Specifying Constraints in SQL: Specifying attribute constraints and attribute defaults Three types of attribute constraints:  Required data: a constraint NOT NULL may be specified if NULL is not permitted for a particular attribute. DnameVARCHAR(10)NOT NULL,  Defaults value: it is possible to define a default value for an attribute by appending the DEFAULT to an attribute definition. DnoINTNOT NULL DEFALT 1,  Domain values constraints: restrict attribute values using CHECK following an attribute or domain definition. Dnumber INT NOT NULL CHECK(Dnumber>0 AND Dnumber<12),

16. 16 Specifying Constraints in SQL: Specifying key and referential integrity constraints PRIMARY KEY clause specifies one or more attributes that make up the primary key of a relation. If the primary key has a single attribute, the clause can follow the attribute directly. CREATE TABLE DEPARTMENT ( DnameVARCHAR(10)NOT NULL, DnumberINTEGERNOT NULL, Mgr_ssnCHAR(9), Mgr_start_dateCHAR(9), PRIMARY KEY (Dnumber), UNIQUE (Dname), FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE );

17. 17 Specifying Constraints in SQL: Specifying key and referential integrity constraints Referential integrity is specified via the FOREIGN KEY clause. FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE (Ssn) SQL rejects any insert, update or delete operation that attempts to create a foreign key value without a matching PK value key. the schema designer can specify an alternative action by attaching a referential triggered action on UPDATE or DELETE operation. Four options are supported when the user attempt to delete or update a PK, and there are matching FKs: CASCADE: automatically delete/update the PK row & all matching (FKs) rows in child table SET NULL: delete/update the PK row & set the FK values to NULL SET DEFAULT: delete/update the PK row & set the FK values to default. Valid only if DEFAULT clause is specified. NO ACTION: rejects the delete operation

18. 18 REFERENTIAL INTEGRITY OPTIONS (contd.) We can specify RESTRICT, CASCADE, SET NULL or SET DEFAULT on referential integrity constraints (foreign keys) CREATE TABLE DEPARTMENT ( DnameVARCHAR(10)NOT NULL, DnumberINTEGERNOT NULL, Mgr_ssnCHAR(9), Mgr_start_dateCHAR(9), PRIMARY KEY (Dnumber), UNIQUE (Dname), FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE (Ssn) ON DELETE SET NULL ON UPDATE CASCADE);

19. 19 CREATE TABLE EMPLOYEE( EnameVARCHAR(30)NOT NULL, EssnCHAR(9), BdateDATE, DnoINTEGER DEFAULT 1, SuperssnCHAR(9), PRIMARY KEY (Essn), FOREIGN KEY (Dno) REFERENCES DEPARTMENT(Dnumber) ON DELETE SET DEFAULT ON UPDATE CASCADE, FOREIGN KEY (SUPERSSN) REFERENCES EMPLOYEE(Ssn) ON DELETE SET NULL ON UPDATE CASCADE); REFERENTIAL INTEGRITY OPTIONS (contd.)