SQL Overview , Oracle Data Type , DDL and Constraints DATE CONSTRAINT emp_hire_date NOT NULL );...

LECTURE8:

SQL OVERVIEW , ORACLE DATA

TYPE , DDL AND CONSTRAINTS

Ref. Chapter6 from

“Database Systems: A Practical Approach to Design, Implementation and Management.”

Thomas Connolly, Carolyn Begg.

I S 2 2 0 : D a t ab a s e F u n d a m e n t a l s

Chapter Objectives

In this chapter you will learn:

The data types supported by the SQL standard.

How to define integrity constraints using SQL including:

required data;

domain constraints;

entity integrity;

referential integrity;

general constraints.

How to use the integrity constraints in the CREATE and ALTER

TABLE

2

The Process of Database Design 3

Conceptual Design (ERD)

Logical Design

(Relational Model)

Physical Design

Create schema

(DDL)

Load Data

(DML)

STRUCTURED QUERY LANGUAGE

SQL

SQL Overview

Official pronunciation is ‘S-Q-L‘ or ( see-qual)

SQL: Structured Query Language

The standard for relational database management systems

(RDBMS) such as Oracle Database.

All SQL statements are instructions to the database.

Easy to learn:

Consists of standard English words, case insensitive

It is a non-procedural language:

you specify what information you require, rather than how to

get it. In other words, SQL does not require you to specify the

access methods to the data

5

SQL in Oracle

• SQL is made up of 4 components:

1. Data Definition Language (DDL)

2. Data Manipulation Language (DML)

3. Data Control Language (DCL)

4. Transaction control statements

6

SQL Components

1. The Data Definition Language (DDL)

This component of the SQL language is used for defining the

database structure and to create and modify tables and

other objects in the database.

For tables there are three main commands:

1. CREATE TABLE tablename : to create a table in the

database

2. DROP TABLE tablename : to remove a table from the

database

3. ALTER TABLE tablename : to add or remove columns from

a table in the database

7

SQL Components

2. The Data Manipulation Language (DML)

component of the SQL language is used for retrieving and

updating data

There are four main commands:

1. SELECT : to select rows of data from a table.

2. INSERT : to insert rows of data into a table.

3. UPDATE : to change rows of data in a table.

4. DELETE : to remove rows of data from a table.

8

SQL Components

3. The Data Control Language (DCL)

This component of the SQL language is used to create

privileges to allow users access to, and manipulation of, the

database.

There are two main commands:

1. GRANT : to grant a privilege to a user

2. REVOKE : to revoke (remove) a privilege from a user

4. Transaction control statements

• COMMIT, ROLLBACK

9

DATA DEFINITION LANGUAGE

( DDL )

Table Creation

10

Data Definition (Creating a table)

CREATING A TABLE Syntax:

Table Name CONDITIONS :

can not exceed 30 characters long

Must begin with an alphabetic character

May contain letters, numbers, $, # and _

Should not be an oracle reserved word

Should be descriptive

11

create table table-name (

column-name1 datatype ,

……..

column-nameN datatype );

Built-In Oracle Data type Summary

Built-in Data type Description Max Size: Oracle 9i/10g

VARCHAR2(size

[BYTE | CHAR]) Variable length character string having

maximum length size bytes.

You must specify size

4000 bytes

minimum is 1

CHAR(size)

Fixed length character data of length size

bytes. This should be used for fixed length

data. Such as codes A100, B102...

2000 bytes

Default and minimum size is 1

byte.

NUMBER(p,s) Number having precision p and scale s. The precision

p can range from 1 to 38.

The scale s can range from -84 to127.

The precision p can range from 1

to 38.

The scale s can range from -84 to

127.

DATE Valid date range from January 1, 4712 BC to

December 31, 9999 AD.

from January 1, 4712 BC to

December 31, 9999 AD.

TIMESTAMP[timePre

csion]

Year, month, and day values of date, as well as

hour,minute, and second values of time,

Accepted values of

fractional_seconds_precision are 0

to 9. (default = 6)

12

NUMBER(p,s)

Syntax for specifying numbers

Number (precision, scale)

Precision is the maximum digits of numbers

Scale specifies the position of decimal point.

E.g.

Number(5) 5 digit integer, ex) 12345

Number(6,2) 6 digit (not including decimal point)

decimal number with 2 digits after the decimal point ,

ex) 1234.56

Can store 1—38 digits precision

13

String

To store strings, you can choose from:

Char (size)

stores fixed-length character strings of up to 2000

characters. Eg. char(10)

Use it to store short strings

Varchar2 (size)

Stores variable-length strings of up to 4000 characters

long. Eg. Varchar2(50)

Preferred for most string types

Must specify the size

String values are quoted with single quotes

Eg ‘12234’, ‘abcd’, ‘a12’

14

Date and time

Oracle uses the date data type to store both date and time

Always uses 7 bytes for date-time data.

Oracle date has rich formats, you need to specify it

SS second 0-59

MI Minute 0-59

HH Hour 1-12

HH24 Military hour 1-24

DD day of month 1-31 (depends on month)

DAY day of the week Sunday-Saturday

D day of the week 1-7

MM month number 1-12

MON month abbreviated Jan—Dec

Month Month spelled out January-December

YY last 2 digits of year eg, 98

YYYY full year value eg, 1998

15

Date and time

Example of date format:

‘dd-mon-yyyy’ 01-dec-2001

‘dd/mm/yyyy’ 01/12/2001

‘mm-dd-yy hh:mi:ss’ 12-01-01 12:30:59

Default format: ‘dd-mon-yyyy’

Current date and time:

Sysdate

16

Example

CREATE TABLE Persons

( P_Id char(5) ,

LastName varchar2(255),

FirstName varchar2(255),

Sex char(2),

);

17

18

Integrity Constraints

An integrity constraint defines a business rule for a table

column.

When enabled, the rule will be enforced by oracle

constraints can be defined at either the table level or the

column level.

If the results of an INSERT or UPDATE statement violate an

integrity constraint, the statement will be rolled back.

Note : If you don’t give the constraint name, the system will

generate a name automatically, but the name is hard for

human understanding.

19

Integrity Constraints

Constraint clauses can appear in the following statements:

1. CREATE TABLE

2. ALTER TABLE

3. CREATE VIEW

4. ALTER VIEW

20

The types of integrity constraint

1. NOT NULL constraint

2. UNIQUE constraint

3. PRIMARY KEY constraint

4. FOREIGN KEY constraint

5. CHECK constraint

21

NOT NULL constraint

The NOT NULL constraint enforces a field to always contain a

value. This means that you cannot insert a new record, or

update a record without adding a value to this field.

Defined at column level ONLY

Syntax:

OR

22

CREATE TABLE table-name (

column-name1 datatype NOT NULL );


column-name1 datatype CONSTRAINT

constraint_name NOT NULL );

CREATE TABLE employees(

employee_id NUMBER(6),

last_name VARCHAR2(25) NOT NULL,

salary NUMBER(8,2),

commission_pct NUMBER(2,2),

hire_date DATE CONSTRAINT emp_hire_date NOT NULL );

Example: NOT NULL

23

System named

User named

SQL NULL

If a column in a table is optional, we can insert a new record or

update an existing record without adding a value to this column. This

means that the field will be saved with a NULL value.

NULL values are treated differently from other values.

NULL is used as a placeholder for unknown or inapplicable values.

Note: It is not possible to compare NULL and 0; they are not

equivalent.

It is not possible to test for NULL values with comparison

operators, such as =, <, or <>.

We will have to use the IS NULL and IS NOT NULL operators

instead.

24

UNIQUE constraint

The UNIQUE constraint prohibits multiple rows from having the same

value in the same column or combination of columns but allows some

values to be null.

Defined at either the table level or the column level

Unique columns are not automatically NOT NULL

Syntax:

25

1- column level


column-name1 datatype UNIQUE );

2- table level


…….

[CONSTRAINT constraint-name] UNIQUE (Columns_list)) ;

The UNIQUE Constraint

26

EMPLOYEES UNIQUE constraint

Allowed

Not allowed: already exists

Example: UNIQUE

The following SQL creates a UNIQUE constraint on the "P_Id" column when the "Persons" table is created:

CREATE TABLE Persons (

P_Id char(5) NOT NULL UNIQUE, LastName varchar2(255) NOT NULL, FirstName varchar2(255), Address varchar2(255),

Telephone varchar2(10), City varchar2(255),

UNIQUE (LastName, FirstName),

CONSTRAINT tel_unique UNIQUE (telephone) );

27

Column level

Table level

Primary Key Constraint

A primary key constraint combines a NOT NULL constraint

and a UNIQUE constraint in a single declaration. That is, it

prohibits multiple rows from having the same value in the

same column or combination of columns and prohibits values

from being null.

A PRIMARY KEY constraint automatically has a UNIQUE

constraint defined on it.


Note that you can have many UNIQUE constraints per table,

but only one PRIMARY KEY constraint per table.

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Primary Key Constraint

OR

29

1- Table level


column-name1 datatype,

……..

column-nameN datatype,

[CONSTRAINT constraint-name] PRIMARY KEY (columns-name));

2- Column level


column-name1 datatype PRIMARY KEY,

……..

column-nameN datatype);

Example: Primary Key

Column Level

CREATE TABLE Department (

Dept_no char(4) PRIMARY KEY,

Dept_name varchar2(25));

OR Table Level


dept_no char(4),

Dept_name varchar2(25),

CONSTRAINT dept_PK PRIMARY KEY (dept_no));

30

Column level

Table level

FOREIGN KEYS constraint

foreign key constraint requires values in one table to match

values in another table.

Syntax:

31

CREATE TABLE table-name ( column-name1 datatype,

……

……

[CONSTRAINT constraint-name] FOREIGN KEY

(Column_name) REFERENCES referenced_table

(column_in_referenced_table) );

Example: Foreign Keys

Create table Employee(

EMPLOYEE_ID NUMBER(3) PRIMARY KEY,

LAST_NAME varchar2(20),

DEPARTMENT_ID NUMBER(3),

CONSTRAINT EMP_Fk FOREIGN KEY (DEPARTMENT_ID)

REFERENCES Department (DEPARTMENT_ID));

32

The FOREIGN KEY Constraint

33

Department

Employee

FOREIGN

KEY

INSERT INTO Not allowed (9 does not

exist)

Allowed

PRIMARY

KEY

90

Referential integrity constraints

When you delete or update a value of the columns referenced

by other tables, the referential integrity constraints may be

violated.

ON DELETE/UPDATE Clause

The ON DELETE / ON UPDATE clause lets you determine

how Oracle Database automatically maintains referential

integrity if you remove or update a referenced primary key

value. If you omit this clause, then Oracle does not allow you

to delete referenced key values in the parent table that

have dependent rows in the child table.

34

referential integrity constraints

Four options are supported when the user attempt to delete the CK and there matching FKs:

ON DELETE/UPDATE CASCADE: delete or update the CK row from the

parent table and all matching FK rows in the child table.

ON DELETE/UPDATE SET NULL: delete or update the CK row from the

parent table and set the FK values to NULL in the child table. This is

valid only if the foreign key columns do not have the NOT NULL

qualifier specified.

ON DELETE/UPDATE SET Default: delete or update the CK row from the

parent table and set the FK values to the specified default value in

the child table. Valid only if DEFAULT constraint is specified

No action: Reject the delete operation from the parent table. This is the

default setting if the ON DELETE rule is omitted.

35

36


DeptNo CHAR(3) PRIMARY KEY,

DeptName VARCHAR2(20) );

CREATE TABLE Employee (

EmpId CHAR(1) PRIMARY KEY,

EmpName VARCHAR2(25),

DeptNo CHAR(3) ,

CONSTRAINT dept_fk FOREIGN KEY (DeptNo) REFERENCES

Department(DeptNo) ON DELETE CASCADE );

delete from Department where DeptNo=103

EmpId EmpName DeptNo

1 Ali 101

2 Sally 101

3 John 103

DeptNo DeptName

101 AAA

102 BBB

103 CCC

PK

FK

DeptNo DeptName

101 AAA

102 BBB


1 Ali 101

2 Sally 101

Department Employee

ON DELETE/UPDATE CASCADE

37







DeptNo CHAR(3) ,


Department(DeptNo) ON DELETE SET NULL );



1 Ali 101

2 Sally 101

3 John 103

DeptNo DeptName

101 AAA

102 BBB

103 CCC

PK

FK

DeptNo DeptName

101 AAA

102 BBB

Department Employee

ON DELETE/UPDATE SET NULL


1 Ali 101

2 Sally 101

3 John NULL

38







DeptNo CHAR(5) Default ‘Empty’,


Department(DeptNo) ON DELETE SET Default);



1 Ali 101

2 Sally 101

3 John 103

DeptNo DeptName

101 AAA

102 BBB

103 CCC

PK

FK

DeptNo DeptName

101 AAA

102 BBB

Department Employee

ON DELETE/UPDATE SET Default


1 Ali 101

2 Sally 101

3 John Empty

Check Constraints

The CHECK constraint is used to limit the value range that can be placed in a column.

If you define a CHECK constraint on a single column it allows only certain values for this column.

If you define a CHECK constraint on a table it can limit the values in certain columns based on values in other columns in the row.


39

Check Constraints

Syntax:

OR

40


column-name1 datatype CHECK (Check_condition) ) ;


…….

…….

[CONSTRAINT constraint-name] CHECK (Check_condition) );

Example : Check

Create table staff(

Staff_no char(3),

Staff_name varchar2(20) not null,

Staff_gender char(1) CHECK (staff_gender in (‘M’, ‘F’)),

Staff_salary number(8,2) not null,

Dept_no char(4),

Constraint staff_pk Primary key (staff_no),

Constraint staff_fk Foreign key (dept_no) references department (dept_no),

Constraint staff_sal CHECK (staff_salary >10000.00));

41

Table level

Column level

Check Condition Examples

1- The Age entered should be greater than or equal 18?

CHECK (AGE >= 18 )

2- the age grade is greater than 18 OR the nationality is ‘Saudi’ ?

CHECK (Age >18 OR nationality=‘Saudi' )

3- the supplier name either IBM or Microsoft or NVIDIA?

CHECK (supplier_name IN ('IBM', 'Microsoft', 'NVIDIA'))

42

DEFAULT constraint

The DEFAULT constraint is used to insert a default value

into a column.

The default value will be added to all new records, if no

other value is specified.

Syntax:

43


column-name1 datatype DEFAULT (Default_value)

);

Example: DEFAULT

Example : The following SQL creates a DEFAULT constraint

on the "City" column when the "Persons" table is created:

CREATE TABLE Persons

(

P_Id char(5) NOT NULL,

LastName varchar2(255) NOT NULL,

FirstName varchar2(255),

Address varchar2(255),

City varchar2(255) DEFAULT 'Sandnes'

);

44

Example : All Constraints

Create table staff(

Staff_no char(3),

Staff_name varchar2(20) NOT NULL,

DateofBirth date,

Staff_nationality char(10) DEFAULT ‘Saudi’,

Staff_salary number(8,2) NOT NULL,

Dept_no char(4),

Constraint staff_pk PRIMARY KEY (staff_no),

Constraint staff_fk FOREIGN KEY (dept_no) references department (dept_no) on delete set null on update cascade,

Constraint staff_sal CHECK (staff_salary >10000.00),

UNIQUE(staff_name, DateofBirth));

45

Summary

46

Constraint Name Type Define it at

NOT NULL Simple( single column) Column-level ONLY

UNIQUE Simple ( single column) Column-level or Table-level

Composite (on multiple ) columns Table-level ONLY

PRIMARY KEY Simple (single column) Column-level or Table-level

Composite (on multiple (columns Table-level ONLY

FOREIGN KEY

Simple ( single column) Column-level or Table-level

Composite (on multiple) columns

Table-level ONLY.

CHECK -- Column-level or Table-level

Defualt -- Column-level ONLY

47


( DDL )

Alter Table

48

ALTER TABLE

ALTER TABLE statement used for changing the structure of a

table once it has been created.

The definition of the ALTER TABLE statement in the ISO

standard consists of six options to:

1. add a new column to a table;

2. drop a column from a table;

3. add a new table constraint;

4. drop a table constraint;

5. set a default for a column;

6. drop a default for a column.

49

Data Definition (Creating a table)

ALTERING A TABLE Syntax:

50

ALTER TABLE TableName

[ ADD columnName dataType ]

[ DROP COLUMN columnName [ RESTRICT | CASCADE]]

[ ADD [ CONSTRAINT [ConstraintName]]tableConstraintDefinition]

[ DROP CONSTRAINT ConstraintName [ RESTRICT | CASCADE]]

[ ALTER columnName SET DEFAULT defaultOption]

[ ALTER columnName DROP DEFAULT]

* Use [CASCADE CONSTRAINTS] to drop PRIMARY KEY column with dependent

integrity constraints.

RESTRICT and CASCADE

RESTRICT

With restrict if any other objects depend for their

existence on continued existence of this table, SQL

does not allow request.

CASCADE

With CASCADE, SQL drops all dependent objects (and objects dependent on these objects).

51

Example

(a) Change the Staff table by removing the default of ‘Assistant’ for the position column and setting the default for the sex column to female (‘F’).

ALTER TABLE Staff

ALTER position DROP DEFAULT;

ALTER TABLE Staff

ALTER sex SET DEFAULT ‘F’;

(b) Change the PropertyForRent table by removing the constraint that staff are not allowed to handle more than 100 properties at a time. Change the Client table by adding a new column representing the preferred number of rooms.

ALTER TABLE PropertyForRent

DROP CONSTRAINT StaffNotHandlingTooMuch;

ALTER TABLE Client

ADD prefNoRooms Number(2);

52

ALTER TABLE - Delete Column or Constraint

create table parent

(id number(2) primary key);

create table child

(id number(2),

Constraint id_fk foreign key (id) references parent(id));

ALTER TABLE parent

drop column id;

ERROR at line 1: ORA-12992: cannot drop parent key column

ALTER TABLE Parent

DROP PRIMARY KEY;

ERROR at line 1:ORA-02273: this unique/primary key is referenced by some foreign keys

53

Use Cascade Constraint

oracle Drops ID in Parent table and removes all

reference constraints to this key. So the foreign key

in Child table is removed.

Alter table parent

drop column id CASCADE CONSTRAINTS;

Table altered.

54


( DDL )

Drop Table

55

DROP TABLES

Pay attention to referential integrity constraints when dropping

tables.

If Cascade Constraints is used, the constraints will be dropped first.

56

Drop table table_name;

OR

Drop table table_name [Cascade Constraints];

Over time, the structure of a database will change; new tables will be created and

some tables will no longer be needed. We can remove a redundant table from the

database using the DROP TABLE statement

Syntax

Example

For example, to remove the PropertyForRent table

we use the command:

DROP TABLE PropertyForRent ;

57

Example

SQL> drop table Department;

drop table Department

*

ERROR at line 1:ORA02449: unique/primary keys in table reference

d by foreign keys

SQL> drop table Department Cascade Constraints ;

Table dropped.

58


1 Ali 101

2 Sally 101

3 John 103

DeptNo DeptName

101 AAA

102 BBB

103 CCC

PK

FK

Employee Department

Viewing Table Structures

To see the structure of a table, type

SQL> describe airlines;

59

DESCRIBE table_name;

or

DESC table_name ;

60

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