Week 4

Lecture 2

Advanced Table Management

Learning Objectives

Create tables with large object (LOB) columns and tables that are index-organized

Understand the tasks involved in table management

Use data dictionary views to find information about tables and their underlying structures

Advanced Table Structures

Table types covered:

Tables with LOB columns:

Store large amount of data in a single column of one row

Can define a separate segment for the LOB

Index-organized tables

Store data in primary key order

Best when queries nearly always use primary key to look up data in the table

Tables with LOB Columns

Types of LOB columns:Internal LOB

• Stored inside the database• Datatypes: BLOB, CLOB, NCLOB

External LOB• Stored outside the database• Datatypes: BFILE• Read-only

Tables with LOB Columns

Example:CREATE TABLE SOUNDBYTES

(ALBUM_ID VARCHAR2(20),

ARTIST VARCHAR2(40),

CD_MUSIC BFILE,

POSTER_SHOT BLOB );

External LOB

Internal LOB

Tables with LOB Columns

New package for updating internal LOBs:DBMS_LOB.LOADBLOBFROMFILE:

Load data into BLOB from external file

DBMS_LOB.LOADCLOBFROMFILE: Load data into CLOB from external file

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Tables with LOB Columns

Semantics of copying LOBs:

Internal LOB uses copy semantics: Copying a LOB from one row or column to another

copies the contents

External LOB uses reference semantics: Copying a LOB from one row or column to another

copies only a pointer to the original location of contents

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LOB Storage

Internal LOBs:• Default stored inline or out of line, by size• Always stored out of line with DISABLE STORAGE IN ROW

External LOBs:• LOB locator stored in the table• LOB data stored in operating system file

LOB Storage

Syntax:CREATE TABLE <tablename> (<other_column_specs>, <LOBcolumnname> <LOBdatatype>)LOB (<LOBcolumnname>) STORE AS <lobsegmentname> (TABLESPACE <tablespacename> ENABLE STORAGE IN ROW|DISABLE STORAGE IN ROW CHUNK <nn> STORAGE (INITIAL <nn> NEXT <nn> MAXEXTENTS UNLIMITED|<nn>) PCTVERSION <nn>|RETENTION LOGGING|NOLOGGING CACHE|NOCACHE);

LOB Storage

Syntax of storage for LOB:STORE AS <lobsegmentname>DISABLE / ENABLE STORAGE IN

ROWSCHUNK <nn>PCTVERSION / RETENTIONLOGGING / NOLOGGINGCACHE / NOCACHE

LOB Storage

Example:

Index-Organized Tables Relational table with primary key

Sorted and stored in key order

Normal relational tables are heap-organized

Stored in b-tree structure

Index-Organized Tables Heap-organized versus Index-

organized

Index-Organized Tables Example:

Index-Organized Tables

Syntax components:ORGANIZATION INDEXOVERFLOWPCTTHRESHOLDINCLUDING <col>TABLESPACE <name>STORAGE (<storage>)

Index-Organized Tables

Example:CREATE TABLE ZIPREFERENCES(ZIPCODE VARCHAR2(10) NOT NULL, CITY VARCHAR2(40) NOT NULL, STATE VARCHAR2(10) NOT NULL, PROVINCE VARCHAR2(10) NOT NULL, COUNTRY VARCHAR2(20) NOT NULL, CONSTRAINT ZIP_PK PRIMARY KEY(ZIPCODE)) ORGANIZATION INDEXTABLESPACE USERSPCTTHRESHOLD 20OVERFLOW TABLESPACE USERSSTORAGE (INITIAL 64K NEXT 32K MAXEXTENTS 50 PCTINCREASE 0);

Overview of Table Management

Types of changes:

Collecting and Refreshing Statistics

Change the storage settings

Reorganize the table online

Drop columns

Truncate or drop the table

Analyzing a Table

Why analyze tables? To give the optimizer up-to-date

information for optimizing queries and other SQL commands

To give you information to help you decide which storage or column settings to change

Analyzing a Table

Oracle's optimizers:

Cost-based optimizerDefaultUses table statistics

Rule-based optimizerOlderUses syntax rules only

Analyzing a Table

Examples ANALYZE command:

ANALYZE TABLE CUSTOMER ESTIMATE STATISTICS

SAMPLE 1000 ROWS;

DBMS_STATS package:

EXECUTE DBMS_STATS.GATHER_TABLE_STATS -

('CLASSMATE','CUSTOMER');

Adjusting Table Storage Structure Syntax of ALTER TABLE command:

ALTER TABLE <schema>.<tablename>PCTFREE <nn> PCTUSED <nn>INITTRANS <nn> MAXTRANS <nn>STORAGE (NEXT <nn> PCTINCREASE <nn> MAXEXTENTS <nn>|UNLIMITED)ALLOCATE EXTENT SIZE <nn> DATAFILE <filename>DEALLOCATE UNUSED KEEP <nn>COMPRESS|NOCOMPRESSMOVE TABLESPACE <tablespacename> STORAGE (INITIAL <nn> NEXT <nn> PCTINCREASE <nn> MAXEXTENTS <nn>|UNLIMITED) COMPRESS|NOCOMPRESS ONLINE

Adjusting Table Storage Structure

Syntax components:PCTFREE <nn> PCTUSED <nn>INITTRANS <nn> MAXTRANS <nn>STORAGE (...)ALLOCATE EXTENTDEALLOCATE UNUSEDCOMPRESSMOVEONLINE

Adjusting Table Storage Structure

Examples: Deallocate unused space:

ALTER TABLE HORSERACE DEALLOCATE UNUSED KEEP 50K;

Change STORAGE setting:

ALTER TABLE CLASSIFIED_AD MOVE TABLESPACE USERS

STORAGE (NEXT 56K);

Reorganizing a Table

DBMS_REDEFINITION package:

Redefine anything in the table Keep old version of the table available

during the change

Reorganizing a Table

DBMS_REDEFINITION steps:

1. Check the table – is it eligible

2. Create interim table with changes you want done

3. Start redefinition process

4. Finish redefinition process

Each step (except #2) is a call to DBMS_REDEFINITION package

Making Other Table Changes

Syntax of the ALTER TABLE command:

ALTER TABLE <schema>.<tablename>

RENAME TO <newname>

LOGGING|NOLOGGING

MONITORING|NOMONITORING

ENABLE|DISABLE ROW MOVEMENT

CACHE|NOCACHE

Making Other Table Changes

Example:

Modify monitoring and cache:

ALTER TABLE EMPLOYEE MONITORING CACHE;

Dropping, Adding, or Modifying a Column in a Table Syntax for ALTER TABLE command:

ALTER TABLE <schema>.<tablename>

RENAME COLUMN <oldcolname> TO <newcolname>

ADD (<colname> <datatype>, ... )

MODIFY (<colname> <datatype>, ... )

DROP (<colname>, <colname>,...)|COLUMN <colname>

CASCADE CONSTRAINTS

SET UNUSED (<colname>,<colname>,...)|COLUMN <colname>

CASCADE CONSTRAINTS

DROP UNUSED COLUMNS

Note: Each of these clauses must be used alone in a single ALTER TABLE command.

Dropping, Adding, or Modifying a Column in a TableExamples: Rename a column:

ALTER TABLE CH08SURGERY RENAME COLUMN PATIENT_FISRT_NAME TO

PATIENT_FIRST_NAME;

Add a column:ALTER TABLE CH08SURGERY ADD (OUTCOME VARCHAR2(40), OPERATING_ROOM_NO

CHAR(4)); Change length of column:

ALTER TABLE CH08SURGERY MODIFY (DOCTOR_NAME VARCHAR2(20));

Truncating and Dropping a Table

TRUNCATE is fast:No redo log entriesNo undo recordsCannot rollbackSyntax:

TRUNCATE TABLE <schema>.<tablename>

DROP STORAGE|REUSE STORAGE

Truncating and Dropping a Table

DROP command:Removes data and structureMust drop constraints that use the

dropped tableExample:

DROP TABLE COPCAR CASCADE CONSTRAINTS;

Querying Table-Related Data Dictionary Views

Querying Table-Related Data Dictionary Views

Querying Table-Related Data Dictionary Views

Example: Look at statistics gathered by

monitoring tables:

SELECT TABLE_NAME, TABLESPACE_NAME, MONITORING,

BLOCKS, EMPTY_BLOCKS

FROM USER_TABLES;

Lecture Summary

LOB data types are either internal LOBS or external LOBS

New features in the DBMS_LOB package simplify loading LOB data

Internal LOB values larger than 4000 bytes are stored out of line in a LOB data segment

Oracle9i works with LOBs by reading and writing one chunk at a time

LOB data segments can also be used to store varray data

Lecture Summary

Index-organized tables require a primary key and store data in order

Optionally split the column data into the main segment and an overflow segment

The ANALYZE command gathers statistics The DBMS_STATS package also gathers

statistics Change a table’s storage parameters using

the ALTER TABLE command

Lecture Summary

DBMS_REDEFINITION restructures a table while keeping it online

ALTER TABLE can do these tasks:Move table to different tablespaceRelease unused spaceRename the tableModify columns (add, change, drop)

TRUNCATE removes rows permanently

Lecture Summary

TRUNCATE can release unused space or keep the space

DROP TABLE removes data and structure

CASCADE CONSTRAINTS if the table being dropped is connected by constraints to other tables