database objects 1

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Database

Objects


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1)Overview on database objects

2)Table and its structure

3)Temporary tables

4)External tables

Agenda


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Database objects

Database objects are the logical entities which Oraclemanages for users.

Users will interact with them through Oracle.

Each object has a unique name.

These objects fit together to form a database.

Database objects are classified into 2 main types:

1)Schema Objects

2)Non Schema Objects


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Introduction to Schema Objects

.

A schema is a collection of logical structures of data, or schema objects.

A schema is owned by a database user and has the same name as

that user.

Each user owns a single schema.

Schema objects are logical structures created by users to contain, or

reference, their data.

Schema objects include structures like tables, views, and indexes etc.

In a relational database, the schema defines the tables, the fields in eachtable, and the relationships between fields and tables.


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illustrates the relationship among

objects, tablespaces, and datafiles.


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Overview of TablesTables are the basic unit of data storage in an Oracle database.

Data is stored in rows and columns.

You define a table with a table name (such as employees) and set of

columns. You give each column a column name (such as employee_id,

last_name, and job_id), a datatype (such as VARCHAR2, DATE, orNUMBER), and a width.

The width can be predetermined by the datatype, as in DATE. If columns

are of the NUMBER datatype, define precision and scale instead of width.

A row is a collection of column information corresponding to a single

record.


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More on tables

After you create a table, insert rows of data usingSQL statements.

Table data can then be queried, deleted, or updated

using SQL.

You can specify rules for each column of a table.

These rules are called integrity constraints.

One example is a NOTNULLintegrity constraint.

This constraint forces the column to contain a value

in every row.



The EMP Table


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When a table is created, a data segment is allocated in atablespace to hold the table's future data.

Controlling the allocation and use of space for a table's data

segment is done in the following ways:

Setting the storage parameters for the data segment.

Setting the PCTFREE and PCTUSED parameters for the

data segment.

How Table Data Is Stored



Managing Storage Parameters

The Storage parameters lets you specify how Oracle Database

should store a database object.

Storage parameters affect both how long it takes to access data

stored in the database and how efficiently space in the

database

The Oracle Database server manages extents for locallymanaged tablespaces.

UNIFORM

AUTOALLOCATE (system-managed)

INITIAL, NEXT, PCTINCREASE, and MINEXTENTS are usedtogether to compute the initial size of the segment. After the

segment size is computed, internal algorithms determine the

size of each extent.



The PCTFREE parameter sets the minimum percentage of a

data block to be reservedas free space for possible updates

to rows that already exist in that block.

The PCTFREE Parameter



After a data block becomes full as determined by PCTFREE,

Oracle does not consider the block for the insertion of new rowsuntil the percentage of the block being used falls below the

parameter PCTUSED.

The PCTUSED Parameter



PCTFREE and PCTUSED work together to optimize the use ofspace in the data blocks of the extents within a data segment.

Figure illustrates the interaction of these two parameters.

How PCTFREE and PCTUSED Work

Together



Format of a Table Row Piece



Temporary TablesAddition to permanent tables, oraclecreates temporary table to hold sessionprivate data.

Each session can only see and modify itsown data.

If the TRUNCATE statement is issuedagainst a temporary table, only the sessionspecific data is truncated. There is no affecton the data of other sessions.



Data in temporary tables isautomatically delete at the end of thedatabase session, even if it ends

abnormally. Indexes ,views and triggers can be

created on temporary tables. Thecontent of the index and the scope of

the index is that same as the databasesession.



.

Temporary tables are ideal for holdingintermediate data used by the current

SQL session.

EX:Select *

into global temporary customer_india

from customer

where state=KARNATAKA



Creation..

The data in a temporary table is privatefor the session that created it and can besession-specific or transaction-specific. Ifthe data is to deleted at the end of the

transaction the table should be definedas follows:CREATE GLOBAL TEMPORARY TABLEmy_temp_table (

column1 NUMBER,column2 NUMBER) ON COMMIT DELETE ROWS;



..

If on the other hand that data shouldbe preserved until the session ends it

should be defined as follows:

CREATE GLOBAL TEMPORARYTABLE my_temp_table (

column1 NUMBER,

column2 NUMBER) ON COMMIT PRESERVE ROWS;



External Tables

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External tables access data in external sources asif it were in a table in the database

External tables are largely used as a convenient

way of moving data into and out of the database.



Creating an external table

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When creating an external table you specify following attributes :

TYPE - specifies the type of external table

The ORACLE_LOADER access driver is the default.

It can perform only data loads, and the data must come from text datafiles.

The ORACLE_DATAPUMP access driver can perform both loads andunloads. The data must come from binary dump files.

DEFAULT DIRECTORY - specifies the default location of files that are read

or written by external tables.

ACCESS PARAMETERS - describe the external data source andimplements the type of external table that was specified.

LOCATION - specifies the location of the external data.

The location is specified as a list of directory objects.


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Creating and Loading an External

Table Using ORACLE_LOADER

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1. Assume your .dat file looks as follows:

56november, 15, 1980 baker mary alice

87december, 20, 1970 roper lisa marie

2. Since an external table's data is in the operating system, its

data file needs to be in a place Oracle can access it. So the first

step is to create a directory and grant access to it.

CREATE DIRECTORY ext_tab_dir AS '/usr/apps/datafiles';

GRANT READ ON DIRECTORY ext_tab_dir TO SCOTT;


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3. Create a traditional table named emp:

CREATE TABLE emp (emp_no CHAR(6), last_name CHAR(25),

first_name CHAR(20), middle_initial CHAR(1));

4. Create an external table named emp_load:

CREATE TABLE emp_load (employee_number CHAR(5),employee_last_name CHAR(20),

employee_first_name CHAR(15),

employee_middle_name CHAR(15))

ORGANIZATION EXTERNAL (type oracle loader default directory ext_tab_dir

ACCESS PARAMETERS (records delimited by

newline fields(employee_number CHAR(2),employee_dob CHAR(20),

employee_last_name CHAR(18),

employee_first_name CHAR(11),

employee_middle_name CHAR(11)))

LOCATION ('info.dat'));


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5.Load the data from the external table emp_load into the table emp:

Insert into emp (emp_no, first_name, middle_initial, last_name)

values(SELECT employee_number, employee_first_name,

substr(employee_middle_name, 1, 1),

employee_last_name FROM emp_load);

6.Perform the following select operation to verify that the information in the

.dat file was loaded into the emp table:

SQL> SELECT * FROM emp; EMP_NO LAST_NAME FIRST_NAME M

------ ------------------------- -------------------- -56 baker mary a

87 roper lisa m


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External Table Restrictions

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An external table does not describe any data that is stored in the database.

An external table does not describe how data is stored in the external source.

This is the function of the access parameters.

An external table cannot load data into a LONG column.

When identifiers (for example, column or table names) are specified

in the external table access parameters, certain values are considered

to be reserved words by the access parameter parser. If a reserved word

is used as an identifier, it must be enclosed in double quotation marks.

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