Chapter 8 Part 1

SQL-99Schema Definition, Constraints, Queries,

and Views

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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

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Database Design

Steps in building a database for an application:

Real-world domain

Conceptualmodel

DBMS data model

Create Schema

(DDL)

Load data(DML)

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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

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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 DOMAIN DROP DOMAIN

CREATE TABLE ALTER TABLE DROP TABLE

CREATE VIEW DROP VIEW

CREATE INDEX DROP INDEX

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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 (

Dname VARCHAR(10) NOT NULL,

Dnumber INTEGER NOT NULL,

Mgr_ssn CHAR(9),

Mgr_start_date CHAR(9) );

SQL Data Definition and Data Type: The CREATE TABLE command in SQL

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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 (

Dname VARCHAR(10) NOT NULL,

Dnumber INTEGER NOT NULL,

Mgr_ssn CHAR(9),

Mgr_start_date CHAR(9),

PRIMARY KEY (Dnumber),

UNIQUE (Dname),

FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE (Ssn));

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Identifiers Names

• May contain A-Z, a-z, 0-9, _

• No longer than 128 characters

• Start with letter

• Cannot contain spaces

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SQL Data Definition and Data Type: Attribute data types and domains in SQL

Type SQL Data Type Used

NumericINTEGER 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

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SQL Data Definition and Data Type: Attribute data types and domains in SQL (contd.)

Type SQL Data Type Used

Bit-stringBIT(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)

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SQL Data Definition and Data Type: Attribute data types and domains in SQL (contd.)

Type SQL Data Type Used

Date_TimeDATE

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

TimestampTIMESTAMP

Has both DATE and TIME components

INTERVALSpecifies a relative value rather than an absolute value. Can be DAY/TIME intervals or YEAR/MONTH intervals

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“COMPANY” Relational Database Schema

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SQL Create Table data definition statements for defining the COMPANY Schema

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

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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.

Dname VARCHAR(10) NOT NULL, Defaults value: it is possible to define a default value for an attribute

by appending the DEFAULT <value> to an attribute definition.

Dno INT NOT 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),

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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 (Dname VARCHAR(10) NOT NULL,Dnumber INTEGER NOT NULL,Mgr_ssn CHAR(9),Mgr_start_date CHAR(9),PRIMARY KEY (Dnumber),UNIQUE (Dname),FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE );

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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

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REFERENTIAL INTEGRITY OPTIONS (contd.)

We can specify RESTRICT, CASCADE, SET NULL or SET DEFAULT on referential integrity constraints (foreign keys)

CREATE TABLE DEPARTMENT ( Dname VARCHAR(10) NOT NULL,

Dnumber INTEGER NOT NULL,Mgr_ssn CHAR(9),Mgr_start_date CHAR(9),

PRIMARY KEY (Dnumber),UNIQUE (Dname),

FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE (Ssn) ON DELETE SET NULL ON UPDATE CASCADE);

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CREATE TABLE EMPLOYEE(Ename VARCHAR(30) NOT NULL,Essn CHAR(9),Bdate DATE,Dno INTEGER DEFAULT 1,Superssn CHAR(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.)