A Guide to Oracle9i1 Creating and Modifying Database Tables Chapter 2.
1 Chapter 2: Creating and Modifying Database Tables.
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Transcript of 1 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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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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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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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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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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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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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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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 Modifying an existing field:ALTER TABLE tablename
MODIFY (fieldname new_field_specification);
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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;