Manage schema object.ppt

7-1 Copyright © 2005, Oracle. All rights reserved.
Managing Schema Objects

Objectives
After completing this lesson, you should be able to do
the following:
• Define schema objects and data types
• Create and modify tables
• Define constraints
• User
• User accounts
• Create indexes
• Naming Schema Object
• Object Namespaces
• Explain the use of temporary tables

Database Schema
 A database schema defines how data is organized
within a relational database.
 This is inclusive of logical constraints such as, table
names, fields, data types, and the relationships between
these entities.

What Is a Schema?
HR schema
HR user
owns
> Schema
Constraints
Indexes
Views
Temp Tables

Schema Objects

Naming Database Objects
• The length of names must be from 1 to 30 bytes,
with these exceptions:
– Names of databases are limited to 8 bytes.
– Names of database links can be as long as
128 bytes.
• Nonquoted names cannot be Oracle-reserved
words.
• Nonquoted names must begin with an alphabetic
character from your database character set.
• Quoted names are not recommended.

Object Namespaces
 A Namespace is a container for a set of
identifiers(symbols or names).
 A namespace defines a group of object types, within
which all names must be uniquely identified, by schema
and name. Objects in different namespaces can share
the same name.
These object types all share the same namespace:
 Tables
 Views
 Sequences
 Private synonyms

Data Types in Tables
Common data types:
• CHAR(size [BYTE|CHAR]): Fixed-length character
data of size bytes or characters
• VARCHAR2(size [BYTE|CHAR]): Variable-length
character string having a maximum length of size
bytes or characters
• DATE: Valid date ranging from January 1, 4712 B.C.
through A.D. December 31, 9999
• NUMBER(p,s): Number with precision p and
scale s

Creating and Modifying Tables
Specify the table
name and schema.
Specify the column names,
data types, and lengths.

DBA User
 A database administrator is a database user of the
database user class DBA.
 Database administrators can manage database users
and database objects.
 The database system administrator is a special
database user of database user class SYSDBA
(administrator).

User Accounts
 For users to access your database, you must create
user accounts and grant appropriate database access
privileges to those accounts.
 A user account is identified by a user name and defines
the attributes of the user, including the following:
 Authentication method
 Password for database authentication
 Default tablespaces for permanent and temporary data
storage
 Tablespace quotas
 Account status (locked or unlocked)
 Password status (expired or not)

Defining Constraints

Constraint Violations
Examples of how a constraint can be violated are:
• Inserting a duplicate primary key value
• Deleting the parent of a child row in a referential
integrity constraint
• Updating a column to a value that is out of the bounds
of a check constraint
101 …
102 …
103 …
101
X … 22
… 49
… 16
… 5
ID AGE
–30

Constraint States
ENABLE
NOVALIDATE
ENABLE
VALIDATE
Existing data
New data
DISABLE
NOVALIDATE
DISABLE
VALIDATE
No DML

Constraint Checking
Case: DML statement, followed by COMMIT
Nondeferred constraints
checked
COMMIT issued
Deferred constraints checked
COMMIT complete
1
3
2
4
Constraints are checked at the time of:
• Statement execution, for nondeferred constraints
• COMMIT, for deferred constraints

Creating Constraints with SQL: Examples
ALTER TABLE countries
ADD (UNIQUE(country_name) ENABLE NOVALIDATE);
ALTER TABLE employees ADD CONSTRAINT pk PRIMARY KEY
(employee_id)
CREATE TABLE t1 (pk NUMBER PRIMARY KEY, fk NUMBER, c1 NUMBER,
c2 NUMBER,
CONSTRAINT ri FOREIGN KEY (fk) REFERENCES t1,CONSTRAINT ck1
CHECK (pk > 0 and c1 > 0));
a
c
b

Viewing the Columns in a Table

Viewing the Contents of a Table

Indexes
22
22
Index Table
Key
Row
pointer
… WHERE key = 22
Schema
Constraints
> Indexes
Views
Temp Tables

Types of Indexes
These are several types of index structures available
to you, depending on the need:
• A B-tree index is in the form of a binary tree and is the
default index type.
• A bitmap index has a bitmap for each distinct value
indexed, and each bit position represents a row that
may or may not contain the indexed value. This is best
for low-cardinality columns.

B-Tree Index
Index entry header
Key column length
Key column value
ROWID
Root
Branch
Leaf
Index entry

Bitmap Indexes
<Blue, 10.0.3, 12.8.3, 1000100100010010100>
<Green, 10.0.3, 12.8.3, 0001010000100100000>
<Red, 10.0.3, 12.8.3, 0100000011000001001>
<Yellow, 10.0.3, 12.8.3, 0010001000001000010>
Key
Start
ROWID
End
ROWID Bitmap
Table
Index
Block 10
Block 11
Block 12
File 3

Index Options
• A unique index ensures that every indexed value is
unique.
• An index can have its key values stored in ascending
or descending order.
• A reverse key index has its key value bytes stored in
reverse order.
• A composite index is one that is based on more than
one column.
• A function-based index is an index based on a
function’s return value.
• A compressed index has repeated key values
removed.

Creating Indexes
CREATE INDEX my_index ON
employees(last_name, first_name);

Temporary Tables
A temporary table:
• Provides storage of data that is automatically cleaned
up when the session or transaction ends
• Provides private storage of data for each session
• Is available to all sessions for use without affecting
each other’s private data
Schema
Constraints
Indexes
Temp Tables

Temporary Tables: Considerations
• Use the GLOBAL TEMPORARY clause to create
temporary tables:
• Use the TRUNCATE TABLE command to delete the
contents of the table.
• You can create the following on temporary tables:
– Indexes
– Views
– Triggers
CREATE GLOBAL TEMPORARY TABLE employees_temp
ON COMMIT PRESERVE ROWS
AS SELECT * FROM employees;

Thank You

Manage schema object.ppt

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