sql-99 : schema definition, constraints, queries, and views

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Ms. Hatoon Al-SagriCCIS – IS Department

SQL-99 :Schema Definition, Constraints, Queries, and Views

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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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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 SCHEMA DROP SCHEMA

CREATE DOMAIN ALTER DOMAIN DROP DOMAIN

CREATE TABLE ALTER TABLE DROP TABLE

CREATE VIEW DROP VIEW

CREATE INDEX DROP INDEX

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Notations

Notations to define SQL statements:

• UPPER-CASE letters represents reserved words

• Lower-case letters represents user-defined words

• | indicates a choice among alternatives; (e.g. a | b | c)

• { } indicates a required element

• [ ] indicates an optional element

• … indicates optional repetition of an item zero or more times

• Underlined words represent default values

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Identifiers

• May contain A-Z, a-z, 0-9, _

• No longer than 128 characters

• Start with letter

• Cannot contain spaces

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Attribute data types and domains in SQL

Type SQL Data Type Used

NumericINTEGER or INT and SMALLINT

Integer numbers of various sizes. NoRoom SMALLINT

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.salary DECIMAL(7,2)

Character-string CHAR(n) or CHARACTER(n)

Fixed length, where n is the number of charactersBno CHAR(4)

VARCHAR(n) or CHAR VARYING(n) or CHARACTER VARYING(n)

Varying length, where n is the maximum number of charactersName VERCHAR(15)

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Type SQL Data Type Used

Bit-string

BIT(n)

Fixed length, where n is the number of bits(0 or 1)BitSt BIT(4)

BIT VARYING (n) Varying length, where n is the maximum number of bits.BitSt BIT VARYING(4)

Boolean

BOOLEAN

There are three values (TRUE,FALSE and UNKNOWN)

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Type SQL Data Type UsedDate_Time

DATE Has ten positions. Made up of year-month-day in the format yyyy-mm-ddViewDate DATE

TIME Made up of hour:minute:second in the format hh:mm:ssViewTime TIME

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.

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Schema concepts in SQL

Schema is a named collection of related database objects (tables,

views, domains, ..) who belong to the same database application.

Specifies a new database schema by giving it a name.

An SQL schema is identified by a schema name and includes an

authorization identifier to indicate the user or account who owns

the schema.

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Creating a DB

SyntaxCREATE SCHEMA [Name | AUTHORIZATION

Identifier]

ExampleCREATE SCHEMA COMPANY AUTHORIZATION Jsmith;

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Domains in SQL

It is possible to specify the data type of each attribute directly or a domain can be declared and the domain name used with the attribute specification.

Syntax: CREATE DOMAIN domainName [AS] datatype [DEFAULT default option] [CHECK (search condition)];

Example:

CREATE DOMAIN SSN_TYPE AS CHAR(9);

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Domains in SQL

Example:CREATE DOMAIN DepartmentNo AS INT;..Dno DepartmentNo,

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Creating a Table

SyntaxCREATE TABLE tablename { ( {columnName dataType [NOT NULL | NULL] [UNIQUE] [DEFAULT defaultOption,]

[CHECK (search condition),] (,…) } [PRIMARY KEY (column (,…) ),] [UNIQUE (column (,…) ),] [FOREIGN KEY (FK column (,…) )

REFERENCES tablename [(CK column (,…))][ON UPDATE ReferentialAction][ON DELETE ReferentialAction], ]

[CHECK (search condition)] ) }

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Creating a Table

Specifies a new relation by giving it a name, and specifying each of its attributes and their data types.

A constraint NOT NULL may be specified on an attribute. Example:

CREATE TABLE DEPARTMENT (Dname VARCHAR(10) NOT NULL,Dnumber INTEGER NOT NULL,Mgr_ssn CHAR(9),Mgr_start_date CHAR(9) );

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DROP Schema

The DROP command can be used to drop the whole schema or drop table and its definition.

Two drop behavior options:– CASCADE, drops all objects associated with schema– RESTRICT, schema must be empty .

SyntaxDROP SCHEMA Name [RESTRICT | CASCADE]

Example:

DROP SCHEMA COMPANY CASCADE;

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DROP Table

The relation can no longer be used in queries, updates, or any other commands since its description no longer exists.

Syntax:DROP TABLE tablename [RESTRICT | CASCADE];

Example: DROP TABLE DEPENDENT CASCADE;

Two drop behavior options:– CASCADE, drop operation drops all column from objects it is referenced by– RESTRICT, drop operation is rejected if the column is referenced by another

database object.

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DROP Domain

Syntax: DROP DOMAIN DomainName [RESTRICT | CASCADE];

RESTRICT, domain must not be used in any existing table, view or assertion.

CASCADE, any column based on the domain is automatically changed to use the underlying data type, column constraint and default clause.

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Specifying attribute constraints

Three types of attribute constraints:1. Required data2. Defaults value3. Domain values constraints

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1. Required data

Null is distinct from blank or zero.When NOT NULL is specified, the system rejects any attempt

to insert a null in the column.

Syntax:columnName dataType [NOT NULL | NULL]

Example:

Dname VARCHAR(10) NOT NULL,

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2. Defaults value

– It is possible to define a default value for an attribute by appending the DEFAULT value to an attribute definition.

– Example:Dno INT NOT NULL DEFALT 1,

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3. Domain values constraints: CHECK Restrict attribute values using CHECK.

Syntax: CHECK (search condition)Example:

Attribute (Column-Based CHECK)

Dnumber INT NOT NULL CHECK(Dnumber>0 AND Dnumber<12),

Domain definition (Column-Based CHECK)

CREATE DOMAIN D_num AS INTEGER CHECK(D_num>0 AND D_num<12);

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Domain values constraints: CHECK Examples

sex CHAR NOT NULL CHECK (sex In (‘M’, ‘F’))

salary DECIMAL NOT NULL CHECK (salary > 10000);

CREATE DOMAIN SexType AS CHAR DEFAULT ‘M’ CHECK (VALUE IN (‘M’, ‘F’));

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Domain values constraints: CHECK

– Other table constraints can be specified through additional CHECK clauses at the end of a CREATE TABLE statement.

– Called tuple-based constraints because they apply for each tuple individually and are checked whenever a tuple is inserted or modified.

–Example:

CHECK (Dept_create_date <= Mgr_start_date)

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Specifying key and referential integrity constraints

PRIMARY KEY UNIQUE FOREIGN KEY

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PRIMARY KEY clause specifies one or more attributes that make up the primary key of a relation.

Syntax:

PRIMARY KEY (attribute (,…))

SQL rejects any operations that attempt to create duplication in the PK column.

PK forbids NULL value.

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If the primary key has a single attribute, the clause can follow the attribute directly.

Example:Dnumber INTEGER NOT NULL,...PRIMARY KEY (Dnumber),

orDnumber INTEGER PRIMARY KEY,

Composite PK: PRIMARY KEY (cno, pno),

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The UNIQUE clause specifies alternate (Secondary).

UNIQUE permits NULL value.

Every column that appears in a UNIQUE clause must also be declared in as NOT NULL.

Syntax: UNIQUE(attribute (,…))

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Example:UNIQUE can appear after a column definition or separately:

Dname VARCHAR(10) NOT NULL,..UNIQUE (Dname),

Or

Dname VARCHAR(10) NOT NULL UNIQUE,

Example:

cno VARCHAR(5) NOT NULL,

pno VARCHAR(5) NOT NULL,

UNIQUE(cno, pno),

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Referential integrity is specified via the FOREIGN KEY clause. FOREIGN KEY clause is defined in the CREATE & ALTER TABLE

statements. Syntax:

FOREIGN KEY (attribute (,…)) REFERENCES table_name [(attribute (,…))] Example:

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.

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REFERENTIAL INTEGRITY OPTIONS

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 or update operation.

Syntax FOREIGN KEY (FK column (,…) ) REFERENCES tablename [(CK column (,…))]

[ON UPDATE [CASCADE | SET NULL| SET DEFAULT| NO ACTION] ]

[ON DELETE [CASCADE | SET NULL| SET DEFAULT| NO ACTION] ]

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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);

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“COMPANY” Relational Database Schema

SQL Create Table data definition statements for defining the COMPANY Schema

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Specifying Constraints in SQL:

Giving Names to constraints:–The constraints can be given a constraint name, following the keyword CONSTRAINT.

– The name must be unique.– In order to modify or delete an existing constraint, it is necessary that the constraint have a name.

Sex CHAR CONSTRAINT SexTypeValidCHECK (sex IN (‘F’, ‘M’) )

Dept CHAR(4) NOT NULL CONSTRAINT DepNoInList CHECK( Dno IN (SELECT Dept FROM DEPARTMENT))

CONSTRAINT IDISKey PRIMARY KEY (SSN)

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Changing a Table Definition

ALTER consists of six options to:

Add a column to table

Drop a column from a table

Add a table constraint

Drop a table constraint

Set a default for a column

Drop a default for a column

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Syntax:ALTER TABLE tablename [ADD [COLUMN] ColumnName dataType [NOT NULL] [UNIQUE] [DEFAULT defaultOption] [CHECK (search condition)] ] [DROP [COLUMN] ColumnName [RESTRICT | CASCADE]] [ADD [CONSTRAINT [Constraint Name]] TableConstraint

Definition] [DROP CONSTRAINT ConstraintName [RESTRICT | CASCADE]] [ALTER ColumnName SET DEFAULT DefaultOption] [ALTER ColumnName DROP DEFAULT];

RESTRICT, drop operation is rejected if the column is referenced by another database object (e.g. view).

CASCADE, drop operation drops all column from objects it is referenced by.

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Example:Add an attribute for keeping track of jobs of staff in the company schemaALTER TABLE staff ADD job VARCHAR(12);

Example:Remove the address attribute from the staff tableALTER TABLE staff DROP address CASCASE;

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Example:Change the staff table by removing the default of ‘Assistant’ for the

position column and setting the default for the sex column to female.

ALTER TABLE staff ALTER position DROP DEFAULT;

ALTER TABLE staff ALTER sex SET DEFAULT ‘F’;

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Example:Change the PropertyForRent table by removing the constraint that

the staff are not allowed more than 100 properties at a time.

ALTER TABLE PropertyForRent

DROP CONSTRAINT StaffNotHandlingTooMuch CASCADE;

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Material for this lecture was obtained from:– Fundamentals of Database Systems, Elmasri and

Navathe, 5th edition, Addison-Wesley, 2007.– Database Systems: A Practical Approach to

Design, Implementation and Management, Thomas Connolly, Carolyn Begg, 3rd edition, 2002.

– The slides of dr. Lilac Safadi, King Saud University.– The slides of T. Abeer Al-Nafjan, Asma AlSaleh

Imam University.

sql-99 : schema definition, constraints, queries, and views

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