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Guide to Oracle 10g
Chapter 2:
Creating and Modifying
Database Tables
1
Database Objects
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An Oracle database consists of multiple
user accounts
Each user account owns database
objects
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Tables
Views
Stored programs
Etc.
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Database Queries
 Query: command to perform
operation on database object
 Create
 Modify
 View
 Delete
 Structured Query Language (SQL)
 Standard query language for
relational databases
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SQL Command Types
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Data Definition Language (DDL)
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Used to create and modify the structure of
database objects
Data Manipulation Language (DML)
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Used to insert, update, delete, and view
database data
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DDL Commands
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Used to create and modify the structure
of database objects
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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
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Used to insert, view, and modify database
data
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INSERT
UPDATE
DELETE
SELECT
DML commands need to be explicitly saved or
rolled back
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COMMIT
ROLLBACK
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User Accounts
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Each Oracle database user has a user
schema
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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
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System Privileges
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Control the operations that the user can perform
within the database
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Connecting to the database (Create Session), creating
new tables, shutting down the database, etc.
Object Privileges
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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
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Oracle database objects must adhere to
the Oracle Naming Standard
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1 to 30 characters long
Must begin with a character
Can contain characters, numbers, and the
symbols $, _, and #
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Defining Database Tables
 To create a table, you must
specify:
 Table name
 Field names
 Field data types
 Field sizes
 Constraints
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Table and Field Names
 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
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Oracle Data Types
 Data type: specifies type of data
stored in a field
 Date, character, number, etc.
 Uses
 Error checking
 Efficient use of storage space
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Oracle Character Data Types
 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)
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Character Data Types
 CHAR
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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)
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Character Data Types
 NCHAR
 Supports 16-digit binary character
codes
 Used for alternate alphabets
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Number Data Type
 NUMBER
 stores values between 10-130 and 10126
 General declaration format:
variable_name NUMBER(precision, scale)
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NUMBER Data Types
 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
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Integer Numbers
 Whole number with no digits to
right of decimal point
 Precision is maximum width
 Scale is omitted
 Sample declaration:
s_age NUMBER (2)
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Fixed Point Numbers
 Contain a specific number of
decimal places
 Precision is maximum width
 Scale is number of decimal places
 Sample declaration:
item_price NUMBER(5, 2)
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Floating Point Numbers
 Contain a variable number of
decimal places
 Precision and scale are omitted
 Sample declaration:
s_GPA NUMBER
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Date Data Type
 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
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Specifying Date and Time
Values
 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
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TIMESTAMP Data Type
 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).
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Interval Year to Month Data
Type
 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.
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Interval Day to Second Data
Type
 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)
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Large Object (LOB) Data
Types
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Binary Large Object (BLOB)
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Character Large Object (CLOB)
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Stores up to 4 GB of character data
BFILE
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Stores up to 4 GB of binary data
Stores a reference to a binary file maintained in
the operating system
NCLOB
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Character LOB that supports 16-bit character code
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Declaring LOB Data Fields
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Item size is not specified
Examples:
item_image BLOB
item_image BFILE
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Creating a Database Table
 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));
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Constraints
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Rules that restrict the values that can
be inserted into a field
Types of constraints
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Integrity: define primary and foreign keys
Value: specify values or ranges of values
that can be inserted
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Constraint Levels
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Table constraint
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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
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Restricts values in a specific column
Example: values in an S_GENDER field
must be ‘M’ or ‘F’
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Constraint Names
 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
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Constraint Names
 Constraint naming convention:
tablename_fieldname_constraintID
 Constraint ID values:
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Primary key: pk
Foreign key: fk
Check condition: cc
Not NULL: nn
Unique: uk
 Example constraint name:
my_students_s_id_pk
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Primary Key Constraints
 Table-level
 Defining a primary key:
CONSTRAINT constraint_name PRIMARY KEY
 Example:
s_id NUMBER(6)
CONSTRAINT student_s_id_pk PRIMARY KEY
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Primary Key Constraints
 Can be defined when field is declared
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Primary Key Constraints
 Can also be defined after all table field
definitions are completed
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Composite Primary Keys
 Syntax:
CONSTRAINT constraint_name
PRIMARY KEY (field1, field2)
 Must be defined after fields that compose
key are defined
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Foreign Key Constraints
 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)
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Foreign Key Constraints
 Can be defined when field is declared
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Foreign Key Constraints
 Can also be defined after all table field
definitions are completed
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Value Constraints
 Column-level
 Restricts data values that can be inserted
in a field
 In general, avoid value constraints because
they make the database very inflexible
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Types of Value Constraints
 Check condition: restricts to specific values
 Example: s_gender (M or F)
CONSTRAINT my_students_s_gender_cc
CHECK (s_gender = ‘M’) OR (s_gender = ‘F’)
 Not NULL: specifies that a field cannot be
NULL
 Example:
CONSTRAINT my_students_s_dob_nn
NOT NULL
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Types of Value Constraints
 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)
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SQL*Plus
 Oracle SQL command line utility for
issuing SQL commands
 Starting SQL*Plus
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Using SQL*Plus
 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’
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Exiting SQL*Plus
 Type exit at SQL> prompt
or
 Click Close button on SQL*Plus
window
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Oracle Help Resources
 Ora.hlp file
 Oracle Technology Network (OTN)
 http://otn.oracle.com
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Viewing Table Information
 Viewing a table’s structure
DESCRIBE table_name;
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Oracle Data Dictionary
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Contains tables that describe the database
structure
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Is automatically updated as users create and
modify tables
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Is in the SYSTEM user schema
Cannot be updated directly
Contains views that allow users to retrieve
information about the database structure
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Data Dictionary Views
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Views present data in different formats
depending on the privileges of the user
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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
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Syntax:
SELECT field1, field2, …
FROM privilege_viewname;
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Summary of Oracle
Data Dictionary Views
OBJECTS
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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Modifying Tables
 Unrestricted actions
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Renaming tables
Adding new columns
Increasing column sizes
Dropping columns
Dropping constraints
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Modifying Tables
 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
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Altering Tables
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Adding a new field:
ALTER TABLE tablename
ADD (fieldname field_specification);
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Altering Tables
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Modifying an existing field:
ALTER TABLE tablename
MODIFY (fieldname new_field_specification);
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Altering Tables
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Deleting an existing field:
ALTER TABLE tablename
DROP COLUMN fieldname;
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Altering Tables
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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
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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;
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