Guide to Oracle 10g
Chapter 2:
Creating and Modifying
Database Tables
Guide to Oracle 10g
1
Database Objects


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

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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Break Time: SQL Plus


Oracle SQL command line utility
for issuing SQL commands
Starting SQL Plus
LOGON to
YOUR
Oracle
Account
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How to Access Your Oracle
Account
1. Click the START button, point to Programs
2. Select Oracle –Oracle10g, then
3. Click Application Development, then
4. Select SQL PLUS
User Name:
Password:
Host string:
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Creating New User Accounts


Done by DBA
Syntax:
CREATE username IDENTIFIED BY password;
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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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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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Creating a Table
CREATE TABLE tablename
(fieldname1 data_type,
(fieldname2 data_type,
…)
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Oracle Data Types
 Data type: specifies type of data
stored in a field
 Date, character, number.
 LONG, RAW, LONG RAW, BLOB
 Uses
 Error checking
 Efficient use of storage space
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Oracle Character Data Types
 VARCHAR2
columnname VARCHAR2(max_size)
Variable-length character strings
Max_size can be between 1 and 4,000 characters
Must specify the size
No trailing blank spaces are added
If more than max_size data is inserted, an error
occurs.
 Example declaration:
student_name VARCHAR2(30)





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Character Data Types
 CHAR
columnname CHAR(max_size)
Fixed-length character data
Max_size can be between 1 and 2000 characters
Max_size is optional. Default is 1.
Adds trailing blank spaces to pad width
If more than max_size data is inserted, an error
occurs.
 Example declaration:
student_gender CHAR(2)





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Character Subtypes
Examples:
VARCHAR2(5)
‘Smith’ or ‘Smi’
CHAR(5)
‘Smith’ or ‘Smi
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Question:
Which query will possibly
generate student information?
s_last VARCHAR2(15);
s_last CHAR(15);
SELECT s_last, s_first,
s_address
FROM student
WHERE s_last = ‘Smith’;
SELECT s_last, s_first,
s_address
FROM student
WHERE s_last = ‘Smith’;


What data type should be used if there is any
chance that all column spaces will NOT be
filled?
Answer: VARCHAR2
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Character Data Types

3. NVARCHAR2 and NCHAR


Analogous to VARCHAR2 and CHAR but
use Unicode rather than ASCII
Used to hold character data in
languages other than English
(Japanese).
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Number Data Type
 NUMBER
 stores negative, positive, fixed, and floating point
numbers 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. It does not include the
decimal point itself or any commas or any
formatting symbols.
 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)

259.99
33.89 (decimal point is not included)
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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
to a known date.
-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

Binary Large Object (BLOB)


Character Large Object (CLOB)


Stores up to 4 GB of character data
BFILE


Stores up to 4 GB of binary data
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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6. Large Object (LOB) Data Types
Ex: f_image BLOB;
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Declaring LOB Data Fields

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


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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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 starts with SYS_Cn. n is a numeric
value.
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Constraint Names
 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
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Constraint Names
10g too
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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
NOTE: faculty TABLE MUST EXIST BEFORE my_students.
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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 unless the user insert an other value
 Example: Must be created in the column declaration, NOT a
separate command beginning with CONSTRAINT.
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)
(Primary key constrain does not allow NULL, but this does)
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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’

Commands are NOT case sensitive.
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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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Create a Table
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Using Notepad

Useful to use Notepad to edit sql
commands
Commands can be edited without
retyping
 Commands can be saved
 Saving multiple sql commands in a
file creates a script

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Study …
Can you create TABLE student now?
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Table Creation Sequence


When creating tables with foreign key
references, create referenced tables
first
Always create tables without foreign
keys before those with foreign keys
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Viewing Table Information
 Viewing a table’s structure
DESCRIBE table_name;
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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
 View: is a db object that the DBMS bases on an actual db
table and which enables the DBMS to present the table
data in a different format based on user needs. It can
serve to hide some table columns in which the user has
no interest or doesn’t have privileges to view.
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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 view_columnname1,
view_columnname2, …
FROM prefix_object;
Try: DESCRIBE user_tables;
to see the details of that
table.
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Viewing Information About Tables





General command:
SELECT view_columnname1, view_columnname2,
…
FROM prefix_object;
view_columnname1, view_columnname2,… are
the name of the fields you want to retrieve from
the view.
prefix: either USER, ALL or DBA.
object: the type of the DB object you are
examining. See next slide for these objects.
Ex: select table_name from user_tables;


Table_name is a field name in the table user_tables.
User_tables is a table saves the names of all the table
you (user) create. Guide to Oracle 10g
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Database Objects with Data Dictionary View
Object Name
Object Type
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_COLUMNS
Table columns that have constraints
IND_COLUMNS
Indexed columns
TAB_COLUMNS
All table
Guide tocolumns
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Viewing Constraints on One Table
Try: DESCRIBE user_constraints;
to see the details of that table.
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Modifying Tables
 Unrestricted actions: some specifications
can always be modified.
 Renaming tables
 Adding new columns
 Increasing column sizes
 Dropping columns
 Dropping constraints
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Modifying Tables
 Restricted actions:specifications modified only in
certain situations
 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
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Deleting and Renaming Tables

To delete:




DROP TABLE [tablename]
Use with caution. It is a restricted actions, can not be dropped if it
contains a foreign key. Delete the constraint and then drop the table or use
cascade.
To delete foreign key constraints, add
“CASCADE CONSTRAINTS”
To rename:



RENAME old_tablename TO new_tablename
DBMS automatically transfers to the new table
integrity constraints, indexes, and privileges that
referenced the old table.
Views and stored program units that reference the
old table name become Invalid.
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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);
Can
only change data type to compatible data
type (i.e. varchar2 to char)
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Altering Tables

Deleting an existing field:
ALTER TABLE tablename
DROP COLUMN fieldname;
ALTER TABLE faculty
ADD (faculty_rank VARCHAR2(4));
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Renaming a Column

To rename a field
ALTER TABLE tablename
RENAME COLUMN old_fieldname TO
new_fieldname;
Ex: ALTER TABLE faculty RENAME COLUMN faculty_rank to f_rank;
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Adding and Deleting Constraints

Add a constraint:
ALTER TABLE tablename
ADD CONSTRAINT constraint_name constraint_definition;

Remove a constraint:
ALTER TABLE tablename
DROP CONSTRAINT constraint_name;
Examples:
ALTER TABLE faculty
ADD CONSTRAINT faculty_f_pin_uk UNIQUE (f_pin);
ALTER TABLE faculty
DROP CONSTRAINT faculty_f_pin_uk;
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Enabling and Disabling Constraints



When modifying a database it can be useful to
disable constraints
Constraints are enabled by default
To disable a constraint:
ALTER TABLE tablename
DISABLE CONSTRAINT constraint_name;

To enable a constraint:
ALTER TABLE tablename
ENABLE CONSTRAINT constraint_name;
1. ALTER TABLE faculty
DISABLE CONSTRAINT faculty_loc_id_fk;
2. ALTER TABLE faculty
ENABLE CONSTRAINT faculty_loc_id_fk;
3. DROP TABLE faculty
CASCADE CONSTRAINTS;
4.
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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;
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Summary

SQL commands include:



To create a table:




Data description language (DDL) commands:
create, modify, Deleted database objects
Data manipulation language (DML) commands:
insert, update, delete, view database data
specify the table name, the name of each data
field, and the data type and size of each data field
Data types ensure correct data values
Constraints restrict values of database fields
SQL*Plus commands are not case sensitive
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Summary



(cont.)
Errors include line number, position,
error code
Use DESCRIBE command to display a
table’s fieldnames and data types
Tables can be modified or deleted but
some changes are restricted
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End Of Chapter 2
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