SQL Basics 1 Presentation

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© 2005 IBM Corporation

Basic SQL – Part IUnderstanding Database Objects

B A Nagabhushan

IBM India Software Labs

In-demand skills for an on demand world



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Agenda• Data Types

• Tables

• Schemas• Table spaces

• Views

• Indexes• Packages

• Buffer Pools

• Transactions• Locks

• Log files

• Creating a database




SQL – An overview• A query language used to query or modify

information from a Relational Database System• Standard Language for an RDBMS as per the

American National Standards Institute (ANSI)

All RDBMS vendors must conform to the ANSIstandards

• Supported on mainframes, minicomputers and

PCs

• Current SQL standard is SQL99




SQL - Components• Data Definition Language (DDL)

Used to create, modify or drop database objects

• Data Manipulation Language (DML)

Used to select, insert, update or delete database data

(records)

• Data Control Language (DCL)

Used to provide data object access control





• Tables


• Views


• Buffer Pools


• Log files





Data Types• Each column in a DB2 table must be associated

with a data type• Data Type indicates the kind of data that is valid

for the column




Data Types - Categories• Two major categories of data types in DB2

Built-in data typesUser-defined data types

• User-defined distinct types

• User-defined structured types

• User-defined reference type





• Tables


• Views


• Buffer Pools


• Log files





Tables• A table is an un-ordered set of rows

• Rows consists of columns• Each column is based on a datatype

• Tables are referenced in the FROM and INTO

clauses of SQL statements

• Three types of tables

Permanent (base) tablesTemporary (declared) tables

Temporary (derived) tables



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• Tables


• Views


• Buffer Pools


• Log files




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Schemas• Used in DB2 to logically group other database

objects

• Most database objects are named using a two-part naming convention – SCHEMA_NAME.OBJECT_NAME

• Example: BBHUSHAN.TABLE1 whereBBHUSHAN is the schema name and TABLE1

is the object name• Implicit schema when no schema is specified

Authorization ID



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Schemas – Contd.• Implicit schema when referenced in an SQL

statement, once again, the authorization ID• CURRENT SCHEMA register contains default

qualifier

Used for unqualified objects referenced for dynamicSQL statements

Can be modified by SET CURRENT SCHEMA

Static SQL statements are qualified by the

authorization ID of the person binding the

application



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Schemas – Contd.• Another SCHEMA qualifier is the

SESSION keywordUsed for temporary tables created and used during a

connection

Only way to reference a declared temporary table inthe SQL is through the SESSION qualifier

If not used, DB2 tries to find the table using the

current schema



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• Tables


• Views


• Buffer Pools


• Log files




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Table Spaces• Logical layer between the database and tables

stored in the database

• Table spaces are created within a database, andtables are created within table spaces

• Two kinds of table spaces:

System Managed Space (SMS)Database Managed Space (DMS)



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Table Spaces – Contd.• By default, tables are created in USERSPACE1

table space

• Any number of table spaces can be created in adatabase, and any number of tables in a tablespace



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• Tables


• Views


• Buffer Pools


• Log files




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Views• Virtual tables derived from one or more tables

or views

• Can be used interchangeably when getting data

• Changes made to the data through a view are

made to the underlying table too

• Views do not contain real data – only definitionis stored in the database

• Used to limit access to sensitive data

• Views can be deletable, updatable, or read-only



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• Tables


• Views


• Buffer Pools


• Log files




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Indexes• Ordered set of pointers to rows in a table

• Associated with individual objects• Any permanent table

• Any declared temporary table• Indexes cannot be defined on a view

• Multiple indexes can be defined on a singletable



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Indexes – Contd.• Indexes are used for two primary reasons

Ensure uniqueness of data values

Improve SQL query performance

• Indexes can also be created on computed

columnsOptimizer can save computation time

• Indexes are maintained automatically by DB2 asdata is inserted, updated, and deleted

Caution: Maintenance overhead can negatively impactperformance of INSERT, UPDATE and DELETE



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Indexes – Contd.• Indexes can be defined in ascending ordescending order

• Indexes can be defined as unique or non-unique

• Indexes can be defined on a single column ormultiple columns

• Indexes can be defined to support forward orreverse scans

• Visual Explain shows if a particular index isused in an SQL statement



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Indexes – Features new in V8• Type-2 indexes eliminates “next-key” locking

Transactions in prior releases could lock an adjacentrecord during processing, resulting in unnecessarydelays in completing transactions

• Indexes can be created on temporary tables.Prior to this, any query against a temporary table

object would result in table scan



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• Tables


• Views


• Buffer Pools


• Log files




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Packages• Contain executable forms of SQL statements.

• Corresponds to a program source moduleOnly the corresponding program source module can

invoke the contents of a package

• Packages contain access plans selected by DB2during the BIND or PREP process.

“Static Binding” as this is performed prior toexecution of SQL statement

• Packages cannot be directly referenced in DML

statements



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Packages – Features new in V8• Packages can now exist in different version

numbers

Multiple versions of the same package can coexist

Advantage: Changes to an existing application andnot invalidate the existing package that users arerunning



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• Tables


• Views


• Buffer Pools


• Log files




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Buffer Pools• Used to cache data pages in memory

Physical I/O can be minimized

• Buffer pools can be assigned to cache only aparticular table space

• Every database must have a buffer pool

IBMDEFAULTBP is the default buffer pool

• Once a buffer pool is created, table spaces can

be assigned to it

• SYSCAT.BUFFERPOOLS catalog view showsthe buffer pools in a database



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• Tables


• Views


• Buffer Pools


• Log files




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Transactions• Sequence of SQL statements executing a single

operation

Same as “Unit of Work”

• A transaction either succeeds or fails

• A transaction starts with the first executablestatement in a program and ends with either anexplicit or implicit COMMIT or ROLLBACK

Implicit COMMIT or ROLLBACK can occur whena DB2 application terminates



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Transactions – Contd.• DB2 allows SAVEPOINTs within a transaction

Allows selective rollback without undoing work prior to the savepoint

Provide control over the work performed by a subsetof SQL statements in a transaction



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• Tables


• Views


• Buffer Pools


• Log files




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Locks• DB2 locking mechanism attempts to avoid

resource conflicts, but with full data integrity

• Transactions obtain locks as SQL statements areprocessed

• Locks are released when the resource is nolonger required or at the end of the transaction

• Locks are stored in memory on the database

server (in locklist)

• Two types of locks – table locks and row locks



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• Tables


• Views


• Buffer Pools


• Log files




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Log Files• As transactions are processed, they are tracked

within log files

• DB2 uses “write-ahead” logging

Changes are first written to the log files, and later,

applied to the physical database tables• Applications should commit their work at

regular intervals to avoid running out of log

space



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Log Files – New features in V8• Log files can be 256GB in size

Log running transactions can finish without fillingup one log file

Even then, DB2 allows chaining of log files so thattheoretically a user should never run out of log

space



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• Tables


• Views


• Buffer Pools

• Transactions

• Locks

• Log files




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Creating a database• A DB2 database must exist before any of the

objects can be created in it

• Database must have a name

• No schema associated with the database

• CREATE DATABASE

• CREATE DATABASE is not a SQL statement – it is aDB2 CLP command

• Next logical step is to create table spaces



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Creating a database• When a database is created without any table

space options, three SMS table spaces are

created by default:SYSCATSPACE – contains system catalog tables

TEMPSPACE1 – contains temporary tables used byDB2

USERSPACE1 – contains the user tables



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Creating a database - SyntaxCREATE DATABASE database-name

[AT DBPARTITIONNUM | [ON drive] [ALIAS database-

alias]

[USING CODESET codeset TERRITORY territory]

[COLLATE USING {SYSTEM | IDENTITY | IDENTITY_16BIT

| COMPATIBILITY | NLSCHAR}]

[NUMSEGS numsegs] [DFT_EXTENT_SZ dft_extentsize][CATALOG TABLESPACE tblspace-defn] [USER TABLESPACE

tblspace-defn]

[TEMPORARY TABLESPACE tblspace-defn] [WITH

"comment-string"]][AUTOCONFIGURE [USING config-keyword value

[{,config-keyword value}...]]

[APPLY {DB ONLY | DB AND DBM | NONE}]]



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Creating a database - Syntaxtblspace-defn:

MANAGED BY { SYSTEM USING ('string' [ {,'string'}

... ] ) |

DATABASE USING ({FILE | DEVICE} 'string' number-of-

pages

[ {,{FILE | DEVICE} 'string' number-of-pages} ... ]

) }

[EXTENTSIZE number-of-pages] [PREFETCHSIZE number-

of-pages]

[OVERHEAD number-of-milliseconds] [TRANSFERRATE

number-of-milliseconds]

[NO FILE SYSTEM CACHING | FILE SYSTEM CACHING]



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Creating a database - Examplecreate database vtutest

on d:

catalog tablespace managed by system

using ('D:\vtutest1\vtucat')

user tablespace managed by system

using ('D:\vtutest2\vtuusr')

temporary tablespace

managed by system

using ('D:\vtutest3\vtutemp')



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Summary• Data Types

• Tables


• Views


• Buffer Pools

• Transactions

• Locks

• Log files




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Your turn…• Exercises posted in the forum

• Answers will be posted 3 days later



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References• Get the most out of DB2 UDB documentation

http://www.ibm.com/developerworks/db2/library/techarticle/ dm-0412chong/

• DB2 Basics: Table spaces and Buffer pools

http://www.ibm.com/developerworks/db2/library/techarticle/ 0212wieser/0212wieser.html

• New to DB2? http://www.ibm.com/developerworks/db2/newto/db2basics.h

tml

• DB2 Universal Database V8.1 for Linux, UNIX,and Windows - Database AdministrationCertification Guide - George Baklarz & Bill Wong

SQL Basics 1 Presentation

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