DB2 - IBM s Relational DBMS

8/4/2019 DB2 - IBM s Relational DBMS

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CTS-PAC Version 1.1 1

DB2 - IBM’s Relational DBMS




Session 1




Topics to be covered in this session

• Introduction to databases - covers their advantages and

the types of databases (time : 30 min)

• Relational database concepts - covers Terminology,ER model , Normalisation, An Introduction to

Database objects, CODD‟s Relational Rules, An

Introduction to SQL.




What is Data ?„A representation of facts or instruction in a form

suitable for communication‟ - IBM Dictionary

What is a Database ?

„Is a repository for stored data‟ - C.J.Date

Introduction to Databases




What is a database system ?An integrated and shared repository for stored data or

collection of stored operational data used by

application systems of some particular enterprise.

Or

„Nothing more than a computer-based record keeping

system‟.

contd...




Advantages of DBMS over File Mngt Sys

•Data redundancy

• Multiple views

• Shared data

• Data independence (logical/physical)

• Data dictionary

• Search versatility

• Cost effective

• Security & Control

• Recovery restart & Backup

• Concurrency




TYPES OF DATABASES (or Models)

• Hierarchical Model

• Network Model

• Relational Model

• Object-Oriented Model




contd...

• HIERARCHICAL

• Top down structure resembling an upside-down

tree

• Parent child relationship

• First logical database model

• Available in legacy systems on Mainframe

computers• Example - IMS




contd...

• NETWORK

• Does not distinguish between parent and child. Any

record type can be assocaited with any number of

arbitrary record types• Enhanced to overcome limitations of Network

model but in reality, there is minimal diffeence due

to frequent enhancements




contd...

• RELATIONAL

• Data stored in table in the form of tables and rows.

• Examples - DB2, Oracle, Sybase, Ingres etc

• OBJECT -ORIENTED MODEL

• Data attributes and methods that operate on those

attributes are encapsulated in structures calledobjects




RELATIONAL DB CONCEPTS




Relational Properties

• Why Relational ? - Relation is a mathematical

term for a table - Hence Relational database „is

perceived‟ by the users as a set of tables.

• All data values are atomic.

• Entries in columns are from the same domain

• Sequence of rows (T-B) is insignificant

• Each row is unique

• Sequence of columns (L-R) is insignificant




Relational Concepts (or Terminology)

• Relation : A table or File

• Tuple : Row contains an entry for each attribute

• Attributes : Columns or the characteristics that

define the entity

• Domain:. A range of values (or Pool)• Entity : Some object about which we wish to store

information

• Null : Represents an unknown value• Atomic : Smallest unit of data; the individual data

value




contd...

• Candidate key : Some attribute (or a set of

attributres) that may uniquely identify each

row(tuple) in the relation(table) This exists only for

a short period of time and the primary and attribute

key take its place.• Primary key : The candidate key that is chosen for

primary attributes to uniquely identify each row.

• Alternate key : The remaining candidate keys that

were not chosen as primary key

• Foreign key : An attrtibute of one relation that might

be a primary key of another relation.




Entity Relationship Model

• E-R model is a logical representation of data for abusiness area

• Represented as entities, relationship between entities

and attributes of both relationships and entities• E-R models are outputs of analysis phase i.e they are

conceptual data models expressed in the form of an E-

R diagram




Normalisation (1NF - 5NF)

• It is done to bring the design of database to astandadized mode

• 1NF : All entities must have a unique identifier, or key,

that can be composed of one or more attributes. Allattributes must be atomic and non repeating.

• 2NF : Partial functional dependencies removed - all

attributes that are not a part of the key must depend on

the entire key for that entity.




contd...

• 3NF : Transitive dependencies removed - attributes thatare not a part of the key must not depend on any non-

key attribute.

• 4NF : Multi valued dependencies removed• 5NF : Remaining anomalies removed




Types of Integrity

• Entity Integrity : Rule states that no column that ispart of a primary key can have a null value

• Referential Integrity : Rule states that every foreign

key in the first table must either match a primary keyvalue in the second table or must be wholly null

• Domain Integrity : Integrity of information allowed in

column




Example of a Relational Structure

CUSTOMER Places ORDERS

ORDERS Has PRODUCTS




The above relations can be interpreted as

follows :

• A Customer can place any number of orders (one-to-many)

• Each order relates to only one customer (one-to-one)

• One order can contain many products (one-to-many)• One Product can be a part of many orders(one-to-

many)




contd...

• In the above example Customer, Order & Product arecalled ENTITIES.

• An Entity may transform into table(s).

• The unique identity for information stored in anENTITY is called a PRIMARY KEY. Eg. Customer-

No uniquely identifies each customer




contd...

A table essentially consists of

• Attributes, which define the characteristics of the

table

• Primary key, which uniquely identifies each row of data stored in a table

• Secondary & Foreign Keys/indexes




contd... Table Definition :

Table „Customer‟ -

Attributes - Customer-No, Cust-name,

Cust-location, Cust-Id, Order-no...

Primary Key - Customer-No

Secondary Key - Cust-Id

Foreign-Key - Order-no




contd...

• The Relationships transform into Foreign Keys. For eg.Customer is related to Orders thru „Order - No‟ which is

the Foreign-key in Customer and Primary key in Order.

So basically the relationship „Places‟ is thru the Order -

No.

• As per the relational integrity the Primary-Key ,Order-

No, for the table „Orders‟ can never be Null, while it

can be so in the table „Customer ‟.




contd...

• Tables exist in Tablespaces. A tablespace can containone or more tables

• Apart from the Primary Key, a table can have many

secondary keys/indexes, which exist in Indexspaces.• These tablespaces and indexspaces together exist in a

Database




contd...

• To do transformations as described above we need atool that will provide a way of creating the tables,

manipulate the data present in these, create

relationships,indexes,tablespace, indexspace and so on.

DB2 provides SQL which performs these functions.

The next part briefly deals with SQL and its functions.

A detailed explanation will be taken up later.




CODDS RELATIONAL RULES

• 1. All information in a relational database isrepresented explicitly at the logical level and in exactly

one way - by values in tables

• 2. Each and every datum(atomic value) in a relational

database is guarenteed to be logically accessible by

resorting to a combination of tablename, primary key

value, and column name




contd...

• 3. Null values are supported for representing missinginformation in a systematic way irrespective of the

datatype.

• 4. The database description is represented at the logical

level in the same way as ordinary data, so that

authorised users can apply the same relational language

to its interrogation as they apply to the regular data.




contd...

• 5.A relational system may support several languagesand various modes of terminal use. However there

must be one language whose statements can express all

of the following items: (1)data definitions (2)view

definitions (3)data manipulation(interactive and by

program)(4) integrity constraints (5) authorisation(6)

transaction boundaries(begin, commit,rollback)




contd...

• 6. All views are theoretically updatable, are alsoupdatable by the system

• 7. The capability of handling a base relation or aderived relation (view) as a single operand applies not

only to the retrierval of of data but also to the

insertion, updation and deletion of data




contd...

• 8. Application programs and terminal activities remainlogically unimpaired whenever any changes are made

in either storage representations or access methods

• 9. Application programs and terminal activities remain

logically unimpaired when information-preserving

changes of any kind that theoretically permit

unimpairment are made to the base tables.




contd...

• 10. Integrity constraints specific to a particularrelational database must be definable in the relational

data sublanguage and storable in the catalog, not in the

application programs.

• 11. The data manipulation sublanguage of a relational

DBMS must enable application programs and inquiries

to remain logically the same whether and wheneverdata are physically centralized or distributed.




contd...

• 12. If a relational system has a low-level(single-record-at-a-time)language, that low level cannot be

used to subvert or bypass the integrity rules and

constraints expressed in the higher-level relational

language(multiple-records-at-a-time)




An introduction to SQL

SQL or Structured Query Language is

• A Powerful language that performs the functions of

data manipulation(DML), data definition(DDL) and

data control or data authorization(DAL/DCL).

• A Non procedural language - the capability to acton a set of data and the lack of need to know the

how to retrieve it. An SQL can perform the

functions of more than a procedure.

• Very flexible




contd...

SQL - Features

• What you want and not how to get it

• Unlike COBOL or 4GL‟s, SQL is coded without

data-navigational instructions.The optimal access

paths are determined by the DBMS. This isadvantageous because the database knows better

how it has stored data than the user.

• Set level processing & multiple row processing




The following are the Operations that can be

performed by a SQL on the database tables :

• Select• Project

• Union

• Intersection• Difference

• Cartesian Product

• Join

• Divide




Session 2




Topics to be covered in this session

• SQL - this is to be dealt here because all other data

objects manipulation, creation and use, involve SQL‟s.

• DB2 objects - Database, Tablespaces & Indexspaces -creation & use, and other terminologies associated with

databases.




Topics dealt with, in SQL

• Definition and Types

• usage of SQL‟s with examples, scalar and column

functions

• Subqueries and Multiple queries, DMLs

• Static & Dynamic SQLs




Structured Query Language - SQL

• Standard query language for RDBMS

• Non procedural lang : Programmer specifies what data

is needed but not how to retrieve it

• Used also to define data structures, control access tothe data and delete occurrences of data

• Uses set-level processing




SQL - Types - based on the functionality

• Data Definition Language (DDL) - CREATE, ALTER,DROP

• Data Manipulation Language (DML) - DELETE,

INSERT, SELECT, UPDATE

• Data Control Language (DCL) - GRANT, REVOKE




SQL - Types

• Production SQL or Ad-Hoc SQL

• Embedded SQL or Stand-alone SQL

• Static or Dynamic SQL




SQL - Selection & Projection

• Select retrieves a specific number of rows from a table

• Projection operation retrieves a specified subset of

columns(but all rows) from the table

Eg : Select Cust-no, Cust-name from Customer;The WHERE clause defines the Predicates for the SQL

operation.

The above WHERE clause can have multiple conditions

using AND & OR.




Select distinct, select in range :

Select Cust-no, Cust-name, Cust-addr

where Cust-no BETWEEN 10000 AND 20000;


where Cust-no NOT BETWEEN 1000 AND 2000;


where Cust-no IN(1000, 2000);




contd...


where Cust-id like/not like „425%‟

Note :- „_‟ for a single char ; „%‟ for a string of charsEscape „ \ ‟ - escape char;if precedes „_‟ or „%‟ overrides

their meaning




contd...

NULL : To check null the syntax is „IS NULL‟ or „IS NOT NULL‟.

Select Cust-no, Cust-name, order-nowhere order-no IS NULL;

However if there are null values for order-no, then these

are always evaluated as a „Not True‟ condition in a

Query.




Order by and Group by clauses :

• Order by sorts retrieved data in the specified order;uses the WHERE clause

• Group by operator causes the table represented by the

FROM clause to be rearranged into groups, such that

within one group all rows have the same value for the

Group by column (not physically in the database). The

Select clause is applied to the grouped data and not to

the original table.Here „HAVING‟ is used to eliminate groups, just like

WHERE is used for rows.




Example :-

Select Order-No, SUM(No-Prodts)

From ORDER

Group by Order-No

Having AVG(No-Prodts) < 10Order by Order-No ;




Functions

• Types are two :

• Column Function

• Scalar Function




Column Functions

• Compute from a group of rows aggregate value for aspecified column(s)

• AVG, COUNT, MAX, MIN, SUM

• Rules for column Functions - Refer Handout




Scalar Functions

• Are applied to a column or expression and operate on asingle value.

• CHAR, DATE, DAY(S), DECIMAL, DIGITS,

FLOAT, HEX, HOUR, INTEGER, LENGTH,

MICROSECOND, MINUTE, MONTH, SECOND,

SUBSTR, TIME, TIMESTAMP, VALUE,

VARGRAPHIC, YEAR

• Rules for Scalar Functions - Refer handout




Complex SQL‟s

• One terms a SQL to be complex when data that is

to be retieved comes from more than one table

• SQL provides two ways of coding a complex SQL

• Subqueries and

• Joins




Subqueries

• Nested select statements• specified using the IN(or NOT IN) predicate, equality

or non-equality predicate(„=„ or „<>„) and comparative

operator(<, <=, >, >=)

• When using the equality, non-equality or comparative

operators, the inner query should return only a single

value




contd...

• Select Cust-No, Cust-Name

From CUSTOMER Where Order-No IN

( Select Order-No From ORDER

Where No-Prdts <5);

• Select Cust-No, Cust-addr

From CUSTOMER Where Order-No =

( Select Order-No From ORDER Where No-Prdts=5);




contd...

• The nested loop statements gives the user the flexibilityfor querying multiple tables

• A specialized form is Correlated Subquery - the nested

Select stmt refers back to the columns in previous

select stmts

• It works on Top-Bottom-Top fashion

• Noncorrelated Subquery works in Bottom-to-Top

fashion




Eg - Correlated Subquery..

• SELECT A.Cust-name A.Cust-addrFROM CUSTOMER A WHERE A.Order-No IN

(SELECT Order-No FROM CUSTOMER B

WHERE A.Cust-id = B.Cust-id)ORDER BY A.Cust-id, A.Cust-no ;




Corelated Subquery using EXISTS clause :

SELECT Cust-No, Cust-name FROM CUSTOMER AWHERE EXISTS (SELECT * FROM ORDER B

WHERE B.Order-No = A.Order-No

AND B.Order-No = 5);




Multiple levels of Subquery

SELECT Cust-no, Cust-name, Cust-addrFROM CUSTOMER A

WHERE Order-no IN

(SELECT order-no FROM ORDER BWHERE Prod-id IN

(SELECT Prod-id FROM PRODUCTS

WHERE Prod-name = „NUTS‟));




Joins

OUTER JOIN : For one or more tables being joined, bothmatching and nonmatching rows are returned.

Duplicate columns may be eliminated

The nonmatching columns will have nulls in them.

INNER JOIN: Here there is a possibility one or more of

the rows from either or both tables being joined will

not be included in the table that results from the joinoperation




DML‟s

INSERT :

Eg: INSERT INTO Tablename(column1,

column2, column3 ,......)VALUES( value1, value2, value3 ,........)

If any column is omitted in an INSERT stmt and that

column is NOT NULL, then INSERT fails; if null it is

set to null




contd...

• If the column is defined as NOT NULL BYDEFAULT, it is set to that default value

• Omitting the list of columns is equivalent to specifying

all values

• SELECT - INSERT

INSERT INTO TEMP (A#, B)

SELECT A#, SUM(B) FROM TEMP1 GROUP

BY A# ;




contd...

UPDATE:

Eg: UPDATE tablename SET Columnname(s) =

scalar expression

WHERE [ condition ]

• Single or Multiple row updates

• Update with a Subquery




contd...

DELETE:

Eg: DELETE FROM Tablename WHERE

[condition ];

• Single or multiple row delete or deletion of all rows




Static SQL

• Hard-coded into an application program• cannot be modified during the program‟s execution

except for changes to the values assigned to the host

variables

• Cursors are used to access set-level data

• The general form is EXEC SQL

[SQL stmts]

END-EXEC.




Dynamic SQL

• Stmts can change throughout the program‟s execution • When the SQL is bound, the application plan or

package that is created does not contain the same info

as that for a static SQL program

• The access paths cannot be determined before

execution




SQL Guidelines :

- Refer handout- Mullins, chapter 2




Topics dealt with, in DB2 objects

• Databases, stogroup, Tablespaces (types, creation and

modification)

• Indexspaces (creation and modification)• some more terms associated with tablespaces




DB2 Objects

• Databases - User & system(catalog)• A collection of logically related objects - like

Tablespaces, Indexspaces, Tables etc.

• not a physical kind of object - may occupy morethan one disk space

• A STOGROUP & BUFFERPOOL must be defined

for each database. Stogroup and user-defined VSAM

are the two storage allocations for a DB2 datasetdefn.




Stogroup

• It is a collection of direct access volumes, all of thesame device type

• The option is defined as a part of tablespace definition

• When a given space needs to be extended, storage isacquired from the

appropriate stogroup




contd...

• In a given database, all the spaces need not have thesame stogroup

• These are, in a sense, the most physical of various

storage objects in DB2

• More than one volume can be defined in a stogroup.

DB2 keeps track of which volume was defined first &

uses that volume.




VCAT Option

• User Defined VSAM datasets have to be definedexplicitly by the AMS utility IDCAMS

• Two types of VSAM datasets are used -ESDS & LDS.

Linear Data set is more efficiently used by DB2

• Vsam datasets defined here are different from the plain

vsam datasets - can access them only thru VSAM

Media Manager

bl




Tablespaces

• Logical address space on secondary storage to hold oneor more tables

• A „SPACE‟ is basically an extendable collection of

pages with each page of size 4K or 32K bytes.

• It is the storage unit for for recovery and reorganizing

purpose

• Three Type of Tablespaces - Simple, Partitioned &

Segmented




Simple Tablespaces

• Can contain more than one stored table• Depending on appln, storing more than one Table

might enable faster retrieval for joins using these tables

• Usually only one is preferred. This is because a singlepage can contain rows from all tables defined in the

database.

• LOAD with replace option deletes all data

S d T bl




Segmented Tablespaces

• Can contain more than one stored table, but in asegemented space

• A „Segment‟ consists of a logically contiguous set of n

pages

• No segement is allowed to contain records for more

than one table

• Sequential access to a particular table is more efficient

d




contd...

• Mass Delete is much more efficient than in any otherTablespace

• Reorganizing the tablespace will restore every table to

its clustered order

• Lock Table on table locks only the table, not the entire

tablespace

• If a table is dropped, the space for that table can be

reclaimed with minimum reorg

P i i d T bl




Partitioned Tablespaces

• Only one table in a partitioned TS; 1 to 64partitions/TS

• It is partitioned in accordance with value ranges for

single or a combination of columns. Hence these

column(s) cannot be updated

td




contd...

• Individual partitions can be independently recoveredand reorganized

• Different partitions can be stored on different storage

groups for efficient access.

Tablespace parameters to be specified for TS




p p p

creation

• Locksize - indicates the type of locking DB2 performsfor the given TS

• Page

•Table

• Tablespace

• ANY - DB2 decides the starting page

td




contd...

• USING - method of storage allocations - Stogroup orVcat

• PCTFREE - % of space available for future inserts

•FREEPAGE - no of pages after which an empty page is

available

• Bufferpool - BPQ, BP1, BP2 & BP32K

• CLOSE - Yes/No - whether the underlying vsam

datasets be closed each time the table is used.Max noof datasets that can be open in DB2 at a time is 10,000

td




contd...

• ERASE - Yes/No - whether physical DASD where theTS reside to be written with binary zeros when the TS

is dropped

• NUMPARTS - For Partitioned Tablespaces

• SEGSIZE - For Segmented Tablespaces

T bl P t f C ti




Table Parameters for Creation

• Column Definition• Format : CREATE TABLE TABLENAME (Column

Definitions)

•PRIMARY KEY(Columns) / FOREIGN KEY

*

• UNIQUE (Colname) (referential constraint)

contd




contd...

• 1. LIKE Table name / View name• 2. IN Database Tablespace Name

• Foreign Key references dbname.table on „relation

condition for delete‟

• Table1 references table2(target) - Table2‟s Primary key

is the foreign key defined in Table1

contd




contd...

• The Condn‟s are CASCADE, RESTRICT & SETNULL (referential constraint for the foreign key

definition)

• Inserting (or updating ) rows in the target is allowed

only if there are no rows in the referencing table

Alter & Drop stmts




Alter & Drop stmts

• ALTER : ALTER TABLE <Tablename>ADD Column Data-type [ not null with default]

• Alter allows primary & Foreign key specifications to

be changed

• It does not support changes to width or data type of a

column or dropping a column

contd




contd...

• DROP : DROP TABLE <Tablename>• Similar stmts are there for INDEX.

Some general rules for RI & Table Parameters




Some general rules for RI & Table Parameters

• Avoid nulls in columns participating inArithmatic logic or comparisons

• Primary key cols cannot be nulls

• Limit referential structures to no more thanthree levels in a direction

contd




contd...

• Use DB2‟s inherent features rather than pgm codedRI‟s.

• Do not use RI‟s on tables build from another RI system

• Consider using Fieldprocs or Editprocs or Validprocs

Index Parameters for Creation




• CREATE INDEX Indexname ON Tablename

(Colnames asc/desc)• CLUSTER

• SUBPAGES

• USING STOGROUP/VCAT (the corresponding name)

• PRIQTY / SECQTY ; ERASE Yes/No

• BUFFERPOOL

• CLOSE - Yes/No

• FREEPAGE

• PCTFREE

Index Guidelines What to do ?




Index Guidelines - What to do ?

1. Consider indexing on columns used inUNION,DISTINCT,GROUP BY, ORDER BY &

WHERE clauses.

2. Limit the indexing of frequently updated columns

3. Create explicitly, a clustering index

4. Create a unique index on the primary key and

indexes on foreign keys

contd




contd...

5. overloading of index when row length of a table tobe accessed is short

6. Atleast one index must be defined for a table with

more than 100 pages

7. Use Multicolumn index rather than a multi-index

(appln dependent); however the latter requires more

DASD .

contd




contd...

8. Create indexes before loading the table.9. Clustering reduces I/O; DB2 optimizer usually tries

to use an index on clustered column before using the

other indexes.

10. Optimize Subpages Parameter

11. Specify Indexspace freespace the same as

tablespace freespace

contd




contd...

12. Use the DEFER option while creating the index.RECOVER INDEX utility can then be used to populate

the index. Recover utility populates index entries

faster.

13. Use different STOGROUP‟s for Tablespaces &

indexspaces

14. Create Critical indexes in a different bufferpool than

the tablespaces.

Index Guidelines - What Not to do ?




Index Guidelines - What Not to do ?

1. Avoid indexing on Variable columns2. Limit the number of indexes on partitioned TS

3. Avoid indexes if the table is very small (< 10 pages) or

it has heavy inserts and deletes and is very small (< 20

pages) or it is accessed with a scan. Avoid defining

redundant indexes

Some more terms & concepts associated with




Tables

VIEWS:• It is a logical derivation of a table from other

table/tables. A View does not exist in its own right.

• They provide a certain amount if logical independence

• They allow the same data to be seen by different users

in different ways

• In DB2 a view that is to accept a update must be

derived from a single base table





Tables

Aliases and Synonyms :Both mean „another name‟ for the table.

however the difference is a synonym is private to the

user who created it. Aliases are used basically foraccessing remote tables (in distributed data

processing), which add a location prefix to their

names.Using aliases creates a shorter name.





Tables

Format:CREATE VIEW <Viewname> (<columns>)

AS Subquery (Subquery - Select from

other Table(s))

. CREATE ALIAS <Aliasname> FOR

<Tablename>

CREATE SYNONYM <Synonymname> FOR

<Tablename>




Session 3




Topic to be covered in this session

• The following topics will be covered in this session

• Application programming using DB2 - 1 day

• Data control Language, SPUFI, QMF, Appln pgmingGuidelines - 0.5 days

Application programming using DB2




Application programming using DB2

• Application environments supporting DB2 :• IMS(Batch/Online), CICS, TSO(Batch/Online)

• CAF - Call Attach Facility

• All DB2 application types can execute concurrently• Host Language support - Cobol, PL/1, C, Fortran or

Assembly lang

Steps involved in creating a DB2 application




Steps involved in creating a DB2 application

• Coding the application• using Host variables

• using Embedded SQL

• using Cursors• issue DCLGEN command

contd...




contd...

• Pre compile the program• Compile & Link edit the program

• Bind

Host Variables




Host Variables

• These are variables(or rather area of storage) defined inthe host language to use the predicates of a DB2 table.

These are referenced in the SQL stmt.

• A means of moving data from and to DB2 tables

• DCLGEN produces host variables, the same as the

columns of the table

Host Variables




Host Variables

Can be used in• „INTO‟ CLAUSE OF SELECT & FETCH

STATEMENTS

• AS INPUT OF „SET‟ CLAUSE OF UPDATE STMTS • AS INPUT FOR THE „VALUES‟ CLAUSE OF

INSERT STATEMENT

• IN WHERE CLAUSE OF SELECT, INSERT,

UPDATE & DELETE

• AS LITERALS IN SELECT LIST OF A SELECT

STATEMENT

Example




a p e

• SELECT Cust_No, Cust_name, Cust_addrFROM CUSTOMER

INTO :H-Cust-No, :H-Cust-name, :H-Cust-addr

WHERE Cust_No = :H_Cust_No;

Embedded SQL statements




Q

• It is like the file I/O• Normally the embedded SQL statements contain the

host variables coded in the INTO or SELECT .... as

shown above

• they are preceded by EXEC SQL

• SELECT, INSERT, UPDATE & DELETE stmts can

be coded inline



Cursors




• DECLARE : name assigned for a particular SQL stmt• OPEN : readies the cursor for row retrieval; sometimes

builds the result table.However it does not assign

values to the host variables

• FETCH : returns data from the results table one row at

a time and assigns the value to specified host variables

• CLOSE : releases all resources used by the cursor

DCLGEN




• issued for a single table• prepares the structure of the table in a COBOL

copybook

• The copybook contains a „SQL DECLARE TABLE‟

stmt along with a working storage host variable defn

for the table

Precompile




p

• searches all the SQL stmts and DB2 related INCLUDEmembers and comments out every SQL stmt in the

program

• the SQL stmts are replaced by a CALL to the DB2

runtime interface module, along with parameters.

• All SQL statements are extracted and put in a Database

Request Module (DBRM)

Contd...




• places a time stamp in the modified source and theDBRM so that these are tied. If there is a mismatch in

this a runtime error of „-818„, timestamp mismatch, is

got

• all DB2 related INCLUDE stmts must be placedbetween EXEC SQL & END EXEC keywords for the

precompiler to recognize them

Compile & Link




p

• modified precompiler COBOL output is compiled• compiled source is link edited to an executable load

module

• appropriate DB2 host language interface module

should also be included in the link edit step(i.e

DSNALI)

Bind




• A type of compiler for SQL statements• It reads the SQL statements from the DBRM and

produces a mechanism to access data (in an efficient

manner) as directed by the SQL statements being

bound

• Checks syntax, checks for correctness of table &

column definitions against the catalog info & performs

authorization validation

Bind Types




yp

• BIND PLAN : accepts as input one or more DBRMsand outputs an application plan containing executable

logic representing optimized access paths to DB2 data.

• BIND PACKAGE : acceps as input a single DBRM

and produces a single package containing theoptimized access path. The PLAN in this case contains

a reference to the physical location of the package(s).

What is a Package ?




• It is a single bound DBRM with optimized access paths• It also contains a location identifier, a collection

identifier and a package identifier

• A package can have multiple versions, each with its

own version identifier

Advantages of Package




• Reduced bind time• can specify bind options at the programmer level

• versioning

• provides for remote data access(in version DB2 V2.3or higher)

Data Control language




• GRANT & REVOKE• GRANT : grants the table privileges, plan & package

privileges, collection privileges, database privileges,

use privileges and system privileges

• user with a SYSADM privilege will be responsible for

overall control of the system

contd...




• Format of GRANT :GRANT SELECT, UPDATE(NAME,NO)

ON TABLE EMPL

TO A, B, C(or PUBLIC);GRANT ALL ON EMPL TO PUBLIC;

GRANT EXECUTE ON PLAN PLANA TO USER;

contd...




• The table privileges allowed are SELECT, UPDATE,DELETE, INSERT, (both base tables & views),

ALTER(Table) & (Create)INDEX(only to base tables)

• There are no specific DROP privilages;the table can be

dropped by its owner or a SYSADM



contd...




• REVOKE : this stmt revokes the privileges given to auser. The user granting the privileges has the authority

to REVOKE also.

• It is not possible to be column specific when revoking

an UPDATE privilege

REVOKE SELECT ON TABLE EMPL FROM

USERA;

For the following refer handout




• List of common SQL return codes and solutions• JCL‟s for bind, compile of DB2 program

Application development guidelines




• Code modular DB2 programs and make them as smallas possible

• use unqualified SQL stmts;this enables movement from

one environment to another(test to prodn)

• Never use Select* in an embedded SQL program;

• use joins rather than subqueries

contd...




• use WHERE clause and filter out data• use cursors when fetching multiple rows, though they

add overheads

• use FOR UPDATE OF clause for UPDATE or

DELETE with cursor - this ensures data integrity.

• use INSERTs minimally ; use LOAD utility instead of

INSERT, if the inserts are not application dependent

QMF - Query Management Facility




• It is an MVS- and VM- based query tool• allows end users to enter SQL queries to produce a

variety of reports and graphs as a result of this query

• QMF queries can be formulated in several ways : by

direct SQL stmts, by means of relational prompted

query interface or by query-by-example (QBE). QBE is

similar to SQL in some ways but more user friendly

SPUFI




• supports the online execution of SQL statements from aTSO terminal

• used for developers to check SQL statements or view

table details

• Spufi menu contains the input file in which the SQL

statements are coded, option for default settings and

editing and the output file.




Session 4




Topics to be covered in this Session

The duration of this session is 0.5 days

• DB2 Utilities

• DB2 Security• DB2 catalog & Optimizer

• Performance tuning

DB2 System administration




• DB2 UTILITIES• CHECK

• COPY, MERGECOPY

• RECOVER

• LOAD

• REORG, RUNSTATS

• EXPLAIN

Check




• checks the integrity of DB2 data structures• checks the referential integrity between two tables and

also checks DB2 indexes for consistency

contd...




• can delete invalid rows and copies them to a exceptiontable

• Use CHECK DATA when loading a table without

specifying the „ENFORCE CONSTRAINTS‟ option or

after the partial recovery of tablespaces in a referentialset

Copy




• used to create an imagecopy for the completetablespace or a partition of the tablespace - full

imagecopy or incremental imagecopy

• every succesful execution of COPY utility places in the

table SYSIBM.SYSCOPY, atleast one row thatindicates the status of the imagecopy

Mergecopy




• The MERGECOPY utility combines multipleincremental image copy data sets into a new full or

incremental image copy data set

Recover




• Standard unit of recovery is a Tablespace• restore DB2 tablespaces and indexes to a specific

instance

• data can be recovered for single pages,pages that

contain I/O errors, a single partition or an entire

tablespace

• indexes are always recovered from the actual table

data, not from image copy and log data, as in the caseof tablespace recovery

Load




• to accomplish bulk inserts into DB2 table• can replace the current data or append to it .i.e. LOAD

DATA REPLACE or LOAD DATA RESUME(S)

• if a job terminates in any phase of LOAD REPLACE

the utility has to be terminated and rerun

contd...




• if a job terminates in any phase other thanUTILINIT(which sets up and initializes the LOAD

utility), the tablespace must be first restored using the

full RECOVER, if LOG NO option of the LOAD was

mentioned.. After the tablespace is restored, the error isto be corrected, the utility terminated and the job rerun.

Reorg




• to reorganize DB2 tables and indexes and therebyimproving their efficiency of access

• reclusters data, resets free space to the amount

specified in the „create ddl‟ statement and deletes and

redefines underlying vsam datasets for stogroupdefined objects

Runstats




• collects statistical information for DB2 tables,tablespaces, partitions, indexes, and columns.

• it can place this info in the catalog tables with DB2

optimizer statistics or DBA monitoring statistics or

with all statistics that have been gathered

• it can be used on specific SQL queries without updting

the current usable statistics

Reorg Job stream




• the total reorg schedule should include• a RUNSTATS job or step : to record current tablespace

and index statistics to DB catalog

• two copy steps for each tablespace being reorganized :

so that data is recoverable. The second copy job is

required after the REORG if it was performed with a

LOG NO option

contd...




• After a REORG is run with LOG NO option, DB2turns on the copy pending status flag for tablespaces

specified in the REORG.

• When LOG NO parameter is specified it is better to

take a imagecopy of the tablespace being reorganizedimmediately after reorg

• a REBIND job for all plans using tables in any of the

tblspaces being organized

Explain




• this feature can be detail the access paths chosen by theDB2 optimizer for SQL statements

• used for performance monitoring

• When EXPLAIN is requested the access paths that the

DB2 chooses are put in coded format into the table

PLAN_TABLE, which is created in the default

database

contd...




• To EXPLAIN a single SQL stmt precede that SQL stmtwith the EXPLAIN Command

EXPALIN ALL SET QUERYNO = integer

FOR SQL stmt

• the other method is specifying EXPLAIN YES with the

Bind command

• then PLAN_TABLE is to be queried to get the required

information.

contd...




• the information provided include the type of access of particualar tables used in the SQL or Package or Plan,

the order in which the tables or joined in a JOIN,

whether SORT is required and so on

• Since the EXPLAIN results are dependent on the DBcatalog, it is better to run RUNSTATS before running a

EXPLAIN

DB2 Security




• LOCKING SERVICES :These are provided by an MVS subsystem called the

IMS resource Lock Manager(IRLM).

It is used to control concurrent access DB2 data,

regardless of whether IMS is present in a system or not.

contd...




• The above is based on Transaction Processing - thesystem component that provides this is „A

TRANSACTION MANAGER‟

• COMMIT & ROLLBACK are key methods of

implementing this

Explicit locking facilities




• the SQL statement LOCK TABLE• the ISOLATION parameter on the BIND PACKAGE

command - the two possible values are RR(„Repeatable

Read‟) & CS(„Cursor Stability‟)

contd...




• the tablespace LOCKSIZE parameter - physically DB2locks data in terms of pages or tables or tablespaces.

This parameter is specified in „CREATE or ALTER

Tablespace‟ option „LOCKSIZE‟. The options are

„Tablespace‟, „Table‟, „Page‟ or „Any‟

contd...




• the ACQUIRE/RELEASE parameters on the BINDPLAN command specifies when table locks(which are

implicitly acquired by DB2) are to be acquired and

released.

• Types : ACQUIRE USE & ACQUIRE ALLOCATE• RELEASE USE & RELEASE ALLOCATE




Session 5

T i t b d i thi S i




Topics to be covered in this Session

The duration of this session is 0.5 days

• DB2 Catalog & Directory

Catalog Tables & the DB2 directory




• Repository for all DB2 objects - contains 43 tables

• Each table maintains data about an aspect of the DB2

environment

• The data refers to info about tablespaces, tables,

indexes, privileges, on utilities run on DB2 and so oneg : SYSIBM.SYSTABLES,

SYSINDEXES/SYSCOLUMNS ......‟

contd...

• Wh t d d DB2 SQL i d th DB2 t l i




• When standard DB2 SQL is used, the DB2 catalog is

either accessed or updated. eg. When a „CREATETABLE‟ stmt is issued the catalog tables

SYSIBM.SYSTABLES, SYSIBM.SYSCOLUMNS &

SYSIBM.SYSFIELDS are updated.

• However the DB2 catalog is semi active only. This isbecause updates to number of rows, the physical order

of the rows for a set of keys and the like are updated

only after running a RUNSTATS utility

• DB2 catalog is integrated - DB2 catalog and DB2

DBMS are inherently bound together

contd...




• It isnonsubvertible

- DB2 catalog cannot be updated behind DB2‟s back. i.e. if a table of 10 columns is

created, it is not possible to go and change the number

of columns directly on the catalog to 15. It has to be

done using the standard SQL statements for droppingand recreating the table

DB2 Optimizer




• Analyzes the SQL statements and determines the mostefficient way to access data - gives Physical data

independence

• It evaluates the following factors : CPU cost, I/O cost,

DB2 catalog statistics & the SQL statement• it estimates CPU time, cost involved in applying

predicates, traversing pages and sorting

contd...




•It estimates the cost of physically retrieving and writing

the data

• The information pertaining to the state of the tables that

will be accessed by the SQL statements are provided

by the Catalog

Performance Tuning




•The performance of an application can be monitored

and enhanced in the application, as well as database

level

• In application side the SQL‟s can be tuned to make

them more efficient, and avoid redundancy• It is better to structure the SQLs so that they perform

only the necessary operations

contd...




•On the database side, the major enhancements can be

done to the definitions of tables, indexes & the

distribution of tablespace and indexspace

• The application run statistics are obtained from

EXPLAIN or DB2PM monitor report



Documents

DB2 - IBM s Relational DBMS