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1Confidential Copyright 2008 Wipro Ltd

Introduction to DB2

What is DB2? A subsystem of the MVS operating system

An abbreviation for IBM Database 2 Was announced in June 1983

Supports SQL (Structured Query Language

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2Confidential Copyright 2008 Wipro Ltd

SQL

The bulk of SQL execution takes place in the DB2 Database Servicesaddress space , which

contains three sub-components: the Relational Data System (RDS), theData Manager, and

the Buffer Manager.

The SQL travels through these three components before the results are

returned to the application. The RDS passes requests to the Data Manager, which

passes requests to the

Buffer Manager. The results trace back from the Buffer Manager to theData Manager to the

RDS. Let's look more closely at the tasks each component handles.

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TYPES OF SQL

Based on Functionality SQL is 3 types.

The Data Control Language (DCL) provides the control stmtsthat govern data security withthe GRANT and REVOKE verbs.

The Data Definition language (DDL) creates and maintains thephysical data structure withthe CREATE, DROP and ALTER sqlverbs

The Data Manipulation Language (DML) accesses and modifiesdata with the SELECT,INSERT, DELETE and UPDATE verbs.

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SQL CREATE TABLE Syntax

CREATE TABLE -

An employee table with fields employee id, name, managername, salary, location can be created by using the followingcommand.

CREATE TABLE employee

(empid SMALLINT NOT NULL,empname CHAR(14),

managerCHAR(14),

salary DECIMAL(9,2)NOT NULL,

location VARCHAR(100) )

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SQL ALTER & DROP TABLE Syntax

ALTER TABLE - A new column can be added to the table by using the ALTER

command.

ALTER TABLE employee

ADD accountnumber DECIMAL(10,0) NOT NULL

Note: you can not use ALTER TABLE command for dropping acolumn.

DROP TABLE-

A TABLE,VIEW can be dropped using DROP statement.

DROP TABLE employee

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The SQL SELECT Statement

The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set.

SQL SELECT Syntax

SELECT column_name(s) FROM tablename

SELECT * FROM table_name

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The SQL SELECT DISTINCT Statement

The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set.

Unique retrieval

SQL SELECT DISTINCT Syntax

SELECT DISTINCT column_name(s) FROM table_name

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The WHERE Clause

The WHERE Clause

The WHERE clause is used to filter records.

WHERE clause is used to retrieve data based on certainconditions.

SQL WHERE Syntax

SELECT column_name(s) FROM table_name WHEREcolumn_name operator value

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The AND & OR Operators

The AND & OR Operators

The AND operator displays a record if both the first conditionand the second condition is true.

The OR operator displays a record if either the first conditionor the second condition is true.

SELECT * FROM Persons WHERE FirstName='Tove' ANDLastName='Svendson'

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The ORDER BY Keyword

The ORDER BY Keyword

The ORDER BY keyword is used to sort the result-set by aspecified ORDER.

The ORDER BY keyword sort the records in ascending order bydefault.

If you want to sort the records in a descending order, you canuse the DESC keyword.

SQL ORDER BY Syntax

SELECT column_name(s) FROM table_name ORDER BYcolumn_name(s) ASC|DESC

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The GROUP BY Keyword

The GROUP BY Keyword

The GROUP BY clause is used for grouping the rows by certaincriteria to retrieve the collective information from the table.

SYNTAX-

SELECT manager, SUM (salary) as Salary

FROM Employee

GROUP BY manager

The above query sums up the salary circulated by eachmanager and displays the total against the manager name.

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INSERT STATEMENT

SQL INSERT Syntax-

The INSERT statement is used for inserting rows into the table.

INSERT INTO table_name VALUES (value1, value2, value3,...)

INSERT INTO table_name (column1, column2, column3,...)VALUES (value1, value2, value3,...)

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The UPDATE Statement

The UPDATE statement is used to update existing records in atable.

SQL UPDATE Syntax-

UPDATE table_name SET column1=value, column2=value2,...WHERE some_column=some_value

Note: The WHERE clause specifies which record or records thatshould be updated. If you omit the WHERE clause, all recordswill be updated!

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The DELETE Statement

The DELETE statement is used to delete rows in a table.

SQL DELETE Syntax

DELETE FROM table_name WHERE some_column=some_value

Note: The WHERE clause specifies which record or records thatshould be deleted. If you omit the WHERE clause, all records

will be deleted!

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SQL Wildcards

SQL wildcards can substitute for one or more characters whensearching for data in a database.

SQL wildcards must be used with the SQL LIKE operator.

With SQL, the following wildcards can be used:

Wild card Description

% A substitute for zero or more characters

_ A substitute for exactly one character

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The IN Operator

The IN operator allows you to specify multiple values in aWHERE clause.

SQL IN Syntax

SELECT column_name(s) FROM table_name WHEREcolumn_name IN (value1,value2,...)

SELECT * FROM Persons WHERE LastName IN('Hansen','Pettersen')

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The BETWEEN Operator

The BETWEEN operator selects a range of data between twovalues. The values can be numbers, text, or dates.

SQL BETWEEN Syntax

SELECT column_name(s) FROM table_name WHEREcolumn_name BETWEEN value1 AND value2

SELECT * FROM Persons WHERE LastName BETWEEN 'Hansen'AND 'Pettersen'

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The UNION AND UNION ALL Keyword

UNION is used to combine two or more select stmt to form a singleresulttable.

UNION is used for represent row

Output should be in sorted order

UNION is used to avoid duplicate.

SELECT empid FROM employee

UNION

SELECT empid FROM department

But if we want to display the result along with the duplicates (as many

times it appears in the tables), we can use UNION ALL. The output is not in sorted order.

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SQL AlIAS AND SYNONYMS

AliaS AND SYNONYMS are alternate name of table Alias is an alternate name that can be used by everyone

synonyms can only be used by creator

SQL AlIAS Syntax for Tables

CREATE ALIAS ALIAS_name for Table_name

SQL SYNONYMS Syntax for Tables

CREATE SYNONYMS SYN_name for Tbl_name

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SQL COLUMN Functions

SQL Column functions return a single value, compute from agroup of rows.

Column functions :

AVG() - Returns the average value

COUNT() - Returns the number of rows

MAX() - Returns the largest value MIN() - Returns the smallest value

SUM() - Returns the sum

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SQL SCALAR Functions

Scalar functions operate on a field to get the required operation done. Scalar functions are applied to acolumn or expressoin & operate on

asingle value.

Scalar functions are :

LENGTH ( ) function is used for finding the length of a field

MONTH ( ) function can be used to retrieve the month part of thedate.

YEAR ( ) function can be used to retrieve the year part of the date.

DATE ( ) function can be used to retrieve the date part of the date.

CONCAT( ) function is used for concatenating strings.

UCASE ( ) function is used for making all characters of a string to

upper case. LCASE ( ) function is used for making all characters of a string to

lowercase.

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SQL JOIN

The art of combining data from multiple table is called joining. Join is mainly representation of column.

TYPES OF JOIN-

2 types of join

1)INNER JOIN.

2)OUTER JOIN.

>LEFT OUTER JOIN

>RIGHT OUTER JOIN

>FULL OUTER JOIN

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SQL INNER JOIN Keyword

The INNER JOIN keyword return rows which are common toboth tables.

SQL INNER JOIN Syntax

SELECT column_name(s) FROM table_name1 INNER JOINtable_name2 ON

table_name1.column_name=table_name2.column_name

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SQL LEFTOUTER JOIN Keyword

The LEFT JOIN keyword returns all rows from the left table(table_name1), even if there are no matches in the right table(table_name2).

SQL LEFT JOIN Syntax

SELECT column_name(s) FROM table_name1 LEFT JOIN

table_name2 ONtable_name1.column_name=table_name2.column_namePS: Insome databases LEFT JOIN is called LEFT OUTER JOIN.

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SQL RIGHTOUTER JOIN Keyword

The RIGHT JOIN keyword Return all rows from the right table(table_name2), even if there are no matches in the left table(table_name1).

SQL RIGHT JOIN Syntax

SELECT column_name(s) FROM table_name1 RIGHT JOIN

table_name2 ONtable_name1.column_name=table_name2.column_name

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SQL FULLOUTER JOIN Keyword

The FULL JOIN keyword return rows when there is a match inone of the tables.

SQL FULL JOIN Syntax

SELECT column_name(s) FROM table_name1 FULL JOINtable_name2 ON

table_name1.column_name=table_name2.column_name

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SQL Constraints

Constraints are used to limit the type of data that can go into atable.

Constraints can be specified when a table is created (with theCREATE TABLE statement) or after the table is created (with theALTER TABLE statement).

We will focus on the following constraints:

NOT NULL

UNIQUE

PRIMARY KEY

FOREIGN KEY

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SQL NOT NULL Constraint

The NOT NULL constraint enforces a column to NOT acceptNULL values.

The NOT NULL constraint enforces a field to always contain avalue. This means that you cannot insert a new record, orupdate a record without adding a value to this field.

The following SQL enforces the "P_Id" column and the"LastName" column to not accept NULL values:

CREATE TABLE Persons ( P_Id int NOT NULL, LastNamevarchar(255) NOT NULL, FirstName varchar(255), Addressvarchar(255), City varchar(255) )

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SQL UNIQUE Constraint

The UNIQUE constraint uniquely identifies each record in a databasetable.

The UNIQUE and PRIMARY KEY constraints both provide a guaranteefor uniqueness for a column or set of columns.

A PRIMARY KEY constraint automatically has a UNIQUE constraintdefined on it.

Note that you can have have many UNIQUE constraints per table, butonly one PRIMARY KEY constraint per table.

SQL UNIQUE Constraint on CREATE TABLE

The following SQL creates a UNIQUE constraint on the "P_Id" columnwhen the "Persons" table is created:

MySQL:

CREATE TABLE Persons ( P_Id int NOT NULL, LastName varchar(255)NOT NULL, FirstName varchar(255), Address varchar(255), Cityvarchar(255), UNIQUE (P_Id) )

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SQL PRIMARY KEY Constraint

The PRIMARY KEY constraint uniquely identifies each record ina database table.

Primary keys must contain unique values.

A primary key column cannot contain NULL values.

Each table should have a primary key, and each table can have

only one primary key. SQL PRIMARY KEY Constraint on CREATE TABLE

The following SQL creates a PRIMARY KEY on the "P_Id" columnwhen the "Persons" table is created:

MySQL:

CREATE TABLE Persons ( P_Id int NOT NULL, LastNamevarchar(255) NOT NULL, FirstName varchar(255), Addressvarchar(255), City varchar(255), PRIMARY KEY (P_Id) )

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SQL FOREIGN KEY Constraint

SQL FOREIGN KEY Constraint A FOREIGN KEY in one table points to a PRIMARY KEY in

another table.

CREATE TABLE Orders ( O_Id int NOT NULL, OrderNo int NOTNULL, P_Id int, PRIMARY KEY (O_Id), FOREIGN KEY (P_Id)

REFERENCES Persons(P_Id) )SQL Server / Oracle / MS Access: CREATE TABLE Orders ( O_Id int NOT NULL PRIMARY KEY,

OrderNo int NOT NULL, P_Id int FOREIGN KEY REFERENCESPersons(P_Id) )

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Indexes

An index can be created in a table to find data more quickly andefficiently.

The users cannot see the indexes, they are just used to speed upsearches/queries.

Note: Updating a table with indexes takes more time than updating atable without (because the indexes also need an update). So youshould only create indexes on columns (and tables) that will befrequently searched against. SQL CREATE INDEX Syntax

Creates an index on a table. Duplicate values are allowed:

CREATE INDEX index_name ON table_name (column_name)SQLCREATE UNIQUE INDEX Syntax

Creates a unique index on a table. Duplicate values are not allowed:

CREATE UNIQUE INDEX index_name ON table_name

(column_name)Note: The syntax for creating indexes varies amongstdifferent databases. Therefore: Check the syntax for creating indexesin your database.

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SQL NULL Values

If a column in a table is optional, we can insert a new record orupdate an existing record without adding a value to thiscolumn. This means that the field will be saved with a NULLvalue.

NULL values are treated differently from other values.

NULL is used as a placeholder for unknown or inapplicablevalues.

Note: It is not possible to compare NULL and 0; they are notequivalent.

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The HAVING Clause

The HAVING clause cheks the properties of each groupin table. Having is used in select stmt with GROUP BY clause.

SQL HAVING Syntax

SELECT column_name, column_function(column_name) FROMtable_name GROUP BY column_name HAVING

column_function(column_name) operator value

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Cursors

Cursor is useful when more than one row of a table to beprocessed

Cursor is nothing but a pointer

Conceptually they are results table used by DB2 to

contain the multiple results of a query.

They are data structures which hold some/all the resultsof a query.

Are defined in the WORKING- STORAGE SECTION/

PROCEDURE DIVISION.

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Cursors

Cursors Notes SELECTs in the general interactive SQL may return any number of rows while

SELECTs in embedded SQL can deal with only one row at a time. A programming device

called a cursor allows the SELECT to find a set of rows but return them one at a time. A cursor

could point to the row to be processed, then move to the next row for processing, and so

on. A cursor needs to be declared using a SELECT statement. It can be declared

both in the WORKING-STORAGE SECTION as well as in the PROCEDURE DIVISION. But, by practice it is done in WORKING-STORAGE SECTION. Cursor definition is done

once. If it is a part of the PROCEDURE DIVISION, then the programmer should have to

separate the

declaration step from the other operations and should make sure that it isdone only once. So by practice it is done in WORKING-STORAGE SECTION.

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Cursors

Operations associated with a Cursor: DECLARE

OPEN

FETCH

CLOSE

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CURSORS

Cursors Notes (continued) The above slide shows the operations associated with a cursor.

The first operation is DECLARE which is used to define the cursor on aspecific set of rows

from a table. Without doing this we cannot form a cursor. But thisdoesnt execute any SQL

statement defined within it. For doing that, we must first open thecursor using the OPEN

command. Then in order to fetch the rows form the result set, theFETCH statement is used

which fetches a single row from the cursor. Finally after performingall the operations, we

need to close the cursor by using the CLOSE statement. All these

operations will be discussed in detail in the coming slides.

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Declaring a Cursor

EXEC SQLDECLARE EMPCUR CURSOR FOR

SELECT EMPNO, NAME, SALARY FROM EMPLOYEE

WHERE EMPNO >:WS-EMPNO

END-EXEC.

Cursors

The first statement is the DECLARE statement. Its a non-executable statement. This is just

the definition, DB2 executes this statement when we open it.Here we specify what should

the cursor contain, or rather the set of rows that are being

retrieved from the table as a result of the SQL query executed. The cursor name follows the

DECLARE word.

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Opening a Cursor

EXEC SQLOPEN EMPCUR

END-EXEC.

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Closing a Cursor

EXEC SQLCLOSE EMPCUR

END-EXEC.

Before using the cursor one must open it. The OPEN statementprepares the SELECT for

execution. It uses the keyword OPEN followed by the cursors name.

When OPEN cursor is done the query is executed and the result set isformed.

The CLOSE statement releases all memory occupied by the cursor. Itis mandatory to close

a cursor before ending a program. After a cursor has been closed, itcan be reopened

without declaring again.

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Fetching results from a cursor

EXEC SQL FETCH EMPCUR

INTO :WS-EMPNO,:WS-NAME,:WS-SALARY

END-EXEC.

Fetching results from a cursor

Cursors (5 of 7)

Remarks:

We get one row at a time.

Only forward READ till SQLCODE = 100.

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Cursors-FETCH

The FETCH statement identifies the cursor to be used andemploys an INTO clause to

indicate the host variables that are to receive the values fromeach row.

A FETCH statement is coded within a loop as we get one row at

a time. DB2 communicates with the programs about processing status

through SQLCODE as

discussed earlier. Like, the program can test for SQLCODE =100 and move out of the loop

when it is encountered.

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Exercise

Which SQL statement is used to extract data from a database?OPEN SELECT GET EXTRACT Which SQL statement is used to update data in a database?

SAVE AS MODIFY

SAVE UPDATE Which SQL statement is used to delete data from a database?

COLLAPSE REMOVE DELETE Which SQL statement is used to insert new data in a database?

ADD RECORD ADD NEW INSERT NEW INSERT INTO

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Exercise

With SQL, how do you select a column named "FirstName" from a table named "Persons"?SELECT Persons.FirstName

EXTRACT FirstName FROM Persons SELECT FirstName FROM Persons . With SQL, how do you select all the columns from a table named "Persons"?

SELECT [all] FROM Persons SELECT * FROM Persons SELECT Persons SELECT *.Persons

With SQL, how do you select all the records from a table named "Persons" where the valueof the column "FirstName" is "Peter"?SELECT [all] FROM Persons WHERE FirstName LIKE 'Peter

SELECT * FROM Persons WHERE FirstName='Peter SELECT * FROM Persons WHERE FirstName'Peter SELECT [all] FROM Persons WHERE FirstName='Peter With SQL, how do you select all the records from a table named "Persons" where the value

of the column "FirstName" starts with an "a"?SELECT * FROM Persons WHERE FirstName LIKE '%a

SELECT * FROM Persons WHERE FirstName LIKE 'a% SELECT * FROM Persons WHERE FirstName='%a% SELECT * FROM Persons WHERE FirstName='a'