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Guide to Oracle 10gGuide to Oracle 10g

Chapter 2:Creating and Modifying Database Tables

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Database Objects An Oracle database consists of

multiple user accounts Each user account owns database

objects Tables Views Stored programs Etc.

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Query: command to perform operation on database object Create Modify View Delete

Structured Query Language (SQL) Standard query language for

relational databases

Database Queries

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SQL Command Types Data Definition Language (DDL)

Used to create and modify the structure of database objects

Data Manipulation Language (DML) Used to insert, update, delete, and

view database data

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DDL Commands Used to create and modify the

structure of database objects CREATE ALTER DROP

DDL commands execute as soon as they are issued, and do not need to be explicitly saved

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DML Commands Used to insert, view, and modify

database data INSERT UPDATE DELETE SELECT

DML commands need to be explicitly saved or rolled back COMMIT ROLLBACK

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User Accounts Each Oracle database user has a

user schema Area in the database where the user’s

database objects are stored Identified by a unique username and

protected by a password Each user schema is granted

specific privileges

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Types of Database Privileges System Privileges

Control the operations that the user can perform within the database

Connecting to the database (Create Session), creating new tables, shutting down the database, etc.

Object Privileges Granted on individual database objects Controls operations that a user can perform on a

specific object (insert data, delete data, etc.) When you create an object in your user schema,

you can then grant object privileges on that object to other database users

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Oracle Naming Standard Oracle database objects must

adhere to the Oracle Naming Standard 1 to 30 characters long Must begin with a character Can contain characters, numbers, and

the symbols $, _, and #

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To create a table, you must specify: Table name Field names Field data types Field sizes Constraints

Defining Database Tables

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Must follow the Oracle Naming Standard

Each table in a user schema must have a unique name within that user schema

Each field in a table must have a unique name within that table

Table and Field Names

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Data type: specifies type of data stored in a field Date, character, number, etc.

Uses Error checking Efficient use of storage space

Oracle Data Types

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VARCHAR2 Variable-length character strings Maximum of 4,000 characters Must specify maximum width

allowed No trailing blank spaces are

added

Example declaration:student_name VARCHAR2(30)

Oracle Character Data Types

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CHAR Fixed-length character data Maximum size 2000 characters Must specify maximum width allowed Adds trailing blank spaces to pad

width

Example declaration:student_gender CHAR(1)

Character Data Types

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NCHAR Supports 16-digit binary

character codes Used for alternate alphabets

Character Data Types

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NUMBER stores values between 10-130 and 10126

General declaration format:variable_name NUMBER(precision, scale)

Number Data Type

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Number type (integer, fixed point, floating point) specified by precision and scale Precision: total number of digits

on either side of the decimal point

Scale: number of digits to right of decimal point

NUMBER Data Types

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Whole number with no digits to right of decimal point

Precision is maximum width Scale is omitted

Sample declaration:s_age NUMBER (2)

Integer Numbers

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Contain a specific number of decimal places

Precision is maximum width Scale is number of decimal

places

Sample declaration:item_price NUMBER(5, 2)

Fixed Point Numbers

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Contain a variable number of decimal places

Precision and scale are omitted

Sample declaration:s_GPA NUMBER

Floating Point Numbers

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DATE Stores dates from 1/1/4712 BC to

12/31/4712 AD Stores both a date and time

component Default date format:

DD-MON-YY HH:MI:SS AM example: 05-JUN-03 12:00:00 AM

Sample declaration:s_dob DATE

Date Data Type

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If no time value is given when a new date is inserted, default value is 12:00:00 AM

If no date value is given when a new time is inserted, default date is first day of current month

Specifying Date and Time Values

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The same as Date DT, but it stores also fractional seconds.

Field Timestamp(Fr_Se_Precision)

E.g: ship_dt Timestamp(2) Fractional Seconds Precision

default value is 6 (If omitted).

TIMESTAMP Data Type

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Field Interval Year(Y_Pr) To Month. Y_Pr: Year Precision(Default: 6). E.g: elapsed Interval Year(2) To

Month. Possible Values:+02-11 :add 2 years and 11 months.-11-4:subtract 11 years and 4 months.

Interval Year to Month Data Type

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Field Interval Day(D_Pr) To Second(Fr_Se_pr).

D_Pr: Day Precision(Default : 2). Fr_Se_Pr: Fractional Seconds

Precision (Default : 6). Possible value:-04 03:20:32.00 (Days

Hours:Minutes:Seconds.Fractions)

Interval Day to Second Data Type

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Large Object (LOB) Data Types Binary Large Object (BLOB)

Stores up to 4 GB of binary data Character Large Object (CLOB)

Stores up to 4 GB of character data BFILE

Stores a reference to a binary file maintained in the operating system

NCLOB Character LOB that supports 16-bit

character code

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Declaring LOB Data Fields Item size is not specified

Examples:item_image BLOB

item_image BFILE

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Syntax:CREATE TABLE table_name

( fieldname1 datatype, fieldname2 datatype, …); Example:CREATE TABLE my_students( s_id NUMBER(6),

s_name VARCHAR2(30), s_dob DATE, s_class CHAR(2));

Creating a Database Table

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Constraints Rules that restrict the values that

can be inserted into a field Types of constraints

Integrity: define primary and foreign keys

Value: specify values or ranges of values that can be inserted

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Constraint Levels Table constraint

Restricts the value of a field with respect to all other table records

Example: primary key value must be unique for each record

Column constraint Restricts values in a specific column Example: values in an S_GENDER

field must be ‘M’ or ‘F’

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Internal name used by DBMS to identify the constraint

Each constraint name in a user schema must be unique

If you do not name a constraint, the system will automatically generate an unintuitive name

Constraint Names

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Constraint naming convention:tablename_fieldname_constraintID

Constraint ID values: Primary key: pk Foreign key: fk Check condition: cc Not NULL: nn Unique: uk

Example constraint name:my_students_s_id_pk

Constraint Names

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Table-level Defining a primary key:

CONSTRAINT constraint_name PRIMARY KEY

Example:s_id NUMBER(6)

CONSTRAINT student_s_id_pk PRIMARY KEY

Primary Key Constraints

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Can be defined when field is declared

Primary Key Constraints

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Can also be defined after all table field definitions are completed

Primary Key Constraints

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Syntax:CONSTRAINT constraint_name

PRIMARY KEY (field1, field2)

Must be defined after fields that compose key are defined

Composite Primary Keys

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Table-level Can only be defined after field is

defined as a primary key in another table

Syntax:CONSTRAINT constraint_name

REFERENCES primary_key_table_name (field_name)

Foreign Key Constraints

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Can be defined when field is declared

Foreign Key Constraints

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Can also be defined after all table field definitions are completed

Foreign Key Constraints

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Column-level Restricts data values that can be

inserted in a field In general, avoid value constraints

because they make the database very inflexible

Value Constraints

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Check condition: restricts to specific values Example: s_gender (M or F)CONSTRAINT my_students_s_gender_ccCHECK (s_gender = ‘M’) OR (s_gender = ‘F’)

Not NULL: specifies that a field cannot be NULL Example: CONSTRAINT my_students_s_dob_nnNOT NULL

Types of Value Constraints

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Default: specifies a default value that is inserted automatically Example:s_state CHAR(2) DEFAULT ‘WI’

Unique Table constraint Specifies that a non-primary key field must have a

unique value CONSTRAINT consultant_c_email_uk UNIQUE (c_email)

Types of Value Constraints

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Oracle SQL command line utility for issuing SQL commands

Starting SQL*Plus

SQL*Plus

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All commands must be terminated with a semicolon

Use a text editor and copy and paste commands

Character data is case sensitive and must be in single quotes‘M’

‘Sarah’

Using SQL*Plus

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Type exit at SQL> promptor

Click Close button on SQL*Plus window

Exiting SQL*Plus

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Ora.hlp file Oracle Technology Network

(OTN) http://otn.oracle.com

Oracle Help Resources

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Viewing a table’s structureDESCRIBE table_name;

Viewing Table Information

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Oracle Data Dictionary Contains tables that describe the

database structure Is in the SYSTEM user schema

Is automatically updated as users create and modify tables Cannot be updated directly

Contains views that allow users to retrieve information about the database structure

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Data Dictionary Views Views present data in different

formats depending on the privileges of the user USER: shows all objects belonging to

the current user ALL: shows all objects belonging to the

current user, as well as objects current user has privileges to manipulate

DBA: allows users with DBA privileges to view objects of all database users

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Querying the Data Dictionary Views Syntax:SELECT field1, field2, …

FROM privilege_viewname;

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Summary of Oracle Data Dictionary ViewsOBJECTS All database objects

TABLES Database tables

INDEXES Table indexes created to improve query performance

VIEWS Database views

SEQUENCES Sequences created to automatically generate surrogate key values

USERS Database users

CONSTRAINTS Table constraints

CONS_CONSTRAINTS

Table columns that have constraints

IND_COLUMNS Indexed columns

TAB_COLUMNS All table columns

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Unrestricted actions Renaming tables Adding new columns Increasing column sizes Dropping columns Dropping constraints

Modifying Tables

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Restricted actions Dropping tables

Only allowed if table does not contain any fields that are referenced as foreign keys, or if foreign key constraints are dropped

Changing a column’s data specification Only allowed if existing data is compatible with

new data specification Decreasing column sizes

Only allowed if column does not contain any data Adding constraints

Only allowed if existing data meets requirements of new constraint

Modifying Tables

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Altering Tables Adding a new field:ALTER TABLE tablename

ADD (fieldname field_specification);

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Altering Tables Modifying an existing field:ALTER TABLE tablename

MODIFY (fieldname new_field_specification);

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Altering Tables Deleting an existing field:ALTER TABLE tablename

DROP COLUMN fieldname;

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Altering Tables Enabling and Disabling Constraints:ALTER TABLE tablename

Enable|Disable CONSTRAINT constraint_name;

E.g: Alter Table faculty

Disable Constraint faculty_f_id_fk;

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Deleting Tables Syntax to delete table if no table

fields are referenced as foreign keys:DROP TABLE tablename;

Syntax to delete table and constraints if table contains fields that are referenced as foreign keys:

DROP TABLE tablename CASCADE CONSTRAINTS;