Guide to Oracle 10g1 Chapter 2: Creating and Modifying Database Tables.

Guide to Oracle 10g 1

Guide to Oracle 10gGuide to Oracle 10g

Chapter 2:Creating and Modifying Database Tables


Database Objects An Oracle database consists of

multiple user accounts Each user account owns database

objects Tables Views Stored programs Etc.


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

Structured Query Language (SQL) Standard query language for

relational databases

Database Queries


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


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


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


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


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


Oracle SQL command line utility for issuing SQL commands

Starting SQL Plus

Break Time: SQL Plus

LOGON to YOUR Oracle Account


How to Access Your Oracle Account

User Name: Password: Host string:

1. Click the START button, point to Programs2. Select Oracle –Oracle10g, then3. Click Application Development, then4. Select SQL PLUS


Creating New User Accounts

Done by DBA Syntax: CREATE username IDENTIFIED BY password;


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 #


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

Defining Database Tables


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


Creating a Table

CREATE TABLE tablename(fieldname1 data_type,(fieldname2 data_type,

…)


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

Oracle Data Types


VARCHAR2columnname 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)

Oracle Character Data Types


CHARcolumnname 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)

Character Data Types


Character Subtypes

Examples:

VARCHAR2(5) ‘Smith’ or ‘Smi’

CHAR(5) ‘Smith’ or ‘Smi ’


Question: Which query will possibly generate student information?

What data type should be used if there is any chance that all column spaces will NOT be filled?

Answer: VARCHAR2

s_last VARCHAR2(15);

SELECT s_last, s_first, s_addressFROM studentWHERE s_last = ‘Smith’;

s_last CHAR(15);

SELECT s_last, s_first, s_addressFROM studentWHERE s_last = ‘Smith’;


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).

Character Data Types


NUMBER stores negative, positive, fixed, and floating

point numbers values between 10-130 and 10126

General declaration format:variable_name NUMBER(precision, scale)

Number Data Type


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

NUMBER Data Types


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


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)

Fixed Point Numbers


Contain a variable number of decimal places

Precision and scale are omitted

Sample declaration:s_GPA NUMBER

Floating Point Numbers


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


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


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


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.

Interval Year to Month 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)

Interval Day to Second Data Type


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


6. Large Object (LOB) Data Types

Ex: f_image BLOB;


Declaring LOB Data Fields Item size is not specified

Examples:item_image BLOB

item_image BFILE


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


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


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’


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.

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

Constraint Names


Constraint Names10g too


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


Can be defined when field is declared



Can also be defined after all table field definitions are completed



Syntax:CONSTRAINT constraint_name

PRIMARY KEY (field1, field2)

Must be defined after fields that compose key are defined

Composite Primary Keys


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


Can be defined when field is declared


NOTE: faculty TABLE MUST EXIST BEFORE my_students.


Can also be defined after all table field definitions are completed



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


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


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)

Types of Value Constraints


Oracle SQL command line utility for issuing SQL commands

Starting SQL*Plus

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.

Using SQL*Plus


Type exit at SQL> promptor

Click Close button on SQL*Plus window

Exiting SQL*Plus


Ora.hlp file Oracle Technology Network

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

Oracle Help Resources


Create a Table


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


Study …

Can you create TABLE student now?


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


Viewing a table’s structureDESCRIBE table_name;

Viewing Table Information


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.


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


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.


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.


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 columns


Viewing Constraints on One Table

Try: DESCRIBE user_constraints; to see the details of that table.


Unrestricted actions: some specifications can always be modified. Renaming tables Adding new columns Increasing column sizes Dropping columns Dropping constraints

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 constraint

Modifying Tables


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.


Altering Tables Adding a new field:ALTER TABLE tablename

ADD (fieldname field_specification);


Altering Tables Modifying an existing field:ALTER TABLE tablenameMODIFY (fieldname new_field_specification);

Can only change data type to compatible data type (i.e. varchar2 to char)


Altering Tables Deleting an existing field:ALTER TABLE tablenameDROP COLUMN fieldname;

ALTER TABLE faculty ADD (faculty_rank VARCHAR2(4));


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;


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 facultyADD CONSTRAINT faculty_f_pin_uk UNIQUE (f_pin);

ALTER TABLE facultyDROP CONSTRAINT faculty_f_pin_uk;


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 tablenameDISABLE CONSTRAINT constraint_name;

To enable a constraint: ALTER TABLE tablename ENABLE CONSTRAINT constraint_name;

1. ALTER TABLE facultyDISABLE CONSTRAINT faculty_loc_id_fk;

2. ALTER TABLE facultyENABLE CONSTRAINT faculty_loc_id_fk;

3. DROP TABLE faculty CASCADE CONSTRAINTS;

4. EXIT;


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;


Summary

SQL commands include: Data description language (DDL)

commands: create, modify, Deleted database objects

Data manipulation language (DML) commands: insert, update, delete, view database data

To create a table: 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


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


End Of Chapter 2

Guide to Oracle 10g1 Chapter 2: Creating and Modifying Database Tables.

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