less06 schema tb

8/14/2019 Less06 Schema Tb

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6Copyright 2005, Oracle. All rights reserved.

Managing Schema Objects


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6-2 Copyright 2005, Oracle. All rights reserved.

Objectives

After completing this lesson, you should be able to dothe following: Define schema objects and data types

Create and modify tables Define constraints View the columns and contents of a table Create indexes

Create views Create sequences Delete the data in a table Explain the use of temporary tables


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What Is a Schema?

HR schemaHR user

owns


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Schemas

Schemas that created as part of the database creationprocess are: SYS

SYSTEM Sample schemas, optionally


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SchemasFull Notes Page


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Accessing Schema Objects


7/466-7 Copyright 2005, Oracle. All rights reserved.

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 128bytes. 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.



Naming Database Objects

Nonquoted names can contain only: Alphanumeric characters from your database

character set The underscore (_) Dollar sign ($) Pound sign (#)

No two objects can have the same name within thesame namespace.



Schema Object Namespaces

Each of the following have their own namespace:

Indexes

ConstraintsClusters

Database triggers

Private database links

Dimensions

The following are in the samenamespace:TablesViewsSequencesPrivate synonymsStand-alone proceduresStand-alone stored functions

PackagesMaterialized viewsUser-defined types



Specifying 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-lengthcharacter string having a maximum length of size bytes or characters

DATE: Valid date range from January 1, 4712 B.C.through A.D. December 31, 9999

NUMBER( p , s ): Number with precision p and scales



Other Data Types

BINARY_FLOAT BINARY_DOUBLE FLOAT INTEGER NCHAR NVARCHAR2 LONG LONG RAW

RAW ROWID UROWID BLOB CLOB NCLOB BFILE TIMESTAMP



Other Data TypesFull Notes Page



Creating and Modifying Tables

Specify the tablename and schema.

Specify the column names,data types, and lengths.



Creating and Modifying TablesFull Notes Page



Understanding Data Integrity

JOB_HISTORYEMPLOYEE_ID(PK,FK)START_DATE (PK)END_DATEJOB_ID (FK)DEPARTMENT_ID (FK)

EMPLOYEESEMPLOYEE_ID (PK)FIRST_NAMELAST_NAMEEMAILPHONE_NUMBERHIRE_DATEJOB_ID (FK)SALARYCOMMISION_PCTMANAGER_ID (FK)DEPARTMENT_ID (FK)

DEPARTMENTSDEPARTMENT_ID (PK)DEPARTMENT_NAMEMANAGER_IDLOCATION_ID (FK)

JOBSJOB_ID (PK)JOB_TITLEMIN_SALARYMAX_SALARY

REGIONSREGION_ID (PK)REGION_NAME

COUNTRIESCOUNTRY_ID (PK)COUNTRY_NAMEREGION_ID (FK)

LOCATIONSLOCATION_ID (PK)STREET_ADDRESSPOSTAL_CODECITYSTATE_PROVINCECOUNTRY_ID (FK)



Understanding Data IntegrityFull Notes Page



Constraint States

ENABLE NOVALIDATE

ENABLE VALIDATE

Existing dataNew data

DISABLE NOVALIDATE

DISABLE VALIDATE

NoDML



Constraint States(Notes Only Slide)



Defining Constraints



Constraint Checking

Case: DML statement, followed by COMMIT

Nondeferred constraintschecked

COMMITissued

Deferred constraints checked

COMMITcomplete

1

3

2

4

Constraints are checked at the time of: Statement execution, for non-deferred 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 ck1CHECK (pk > 0 and c1 > 0));

a

c

b



Viewing the Columns in a Table



Viewing the Contents of a Table



Actions with Tables



Dropping a Table

Dropping a table removes: Data Table structure

Database triggers Corresponding indexes Associated object privileges

Optional clauses for the DROP TABLE statement:

CASCADE CONSTRAINTS: Dependent referentialintegrity constraints

PURGE: No flashback possible

DROP TABLE hr.employees PURGE;



Truncating a Table

Truncating a table makes its row data unavailable,and optionally releases used space.

Corresponding indexes are truncated.

TRUNCATE TABLE hr.employees;


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Indexes

22

22

Index Table

KeyRow

pointer

WHERE key = 22


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Types of Indexes

These are several types of index structures availableto 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 arow that may or may not contain the indexedvalue. This is best for low-cardinality columns.


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B-Tree Index

Index entry header Key column length

Key column value

ROWID

Root

Branch

Leaf

Index entry


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Bitmap Indexes

key

start

ROWID

end

ROWID bitmap

Table

Index

Block 10

Block 11

Block 12

File 3


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Index Options

A unique index ensures that every indexed valueis unique.

An index can have its key values stored inascending or descending order.

A reverse key index has its key value bytes storedin reverse order.

A function-based index is an index based on afunctions return value.

A compressed index has repeated key valuesremoved.


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Creating Indexes

CREATE INDEX my_index ONemployees(last_name, first_name);


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What Is a View?

CREATE VIEW v AS SELECT location_id, country_name FROM locations l, countries c

WHERE l.country_id = c.country_id AND c.country_id in('AU','BR');

COUNTRYtable

LOCATION table

View


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Creating Views


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Sequences

A sequence is a mechanism for automaticallygenerating integers that are guaranteed to be unique.

10011002

10031004

10051006

10071008

1009

10101011

1000000 12

34

56

78

999995999990

999985999980

999975


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Sequences

A sequence has a name, which is how it isreferenced when the next value is requested.

A sequence is not associated with any particular table or column.

The order of progression can be ascending or descending.

The interval between numbers can be of any size. Sequence values can be cached to improve

performance. A sequence can cycle when a limit is reached.


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Creating a Sequence


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What Is a Sequence?Full Notes Page


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Using a Sequence


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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 others private data


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Temporary Tables(Notes only slide)


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Temporary Tables: Considerations

Use the GLOBAL TEMPORARYclause to createtemporary tables:

Use the TRUNCATE TABLE command to delete thecontents 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;


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Summary

In this lesson, you should have learned how to: Define schema objects and data types Create and modify tables

Define constraints View the columns and contents of a table Explain the usage of types of indexes Create views

Create and use sequences Delete the data in a table in the most efficient

manner Explain the use of temporary tables


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Practice Overview:Administering Schema Objects

This practice covers the following topics: Creating tables with columns Creating constraints:

Primary key Check Foreign key

Creating indexes

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