working with db2 data using sql and xquery

8/6/2019 Working With DB2 Data Using SQL and XQuery

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IBM DB2 9

2008 IBM Corporation

Section -4) Working with DB2 DataWorking with DB2 Datausing SQL and XQueryusing SQL and XQuery

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Section 4Section 4 -- Working with DB2 Data usingWorking with DB2 Data using

SQL and XQuery (23.5%)SQL and XQuery (23.5%) Given a DML SQL statement, ability to identify resultsGiven a DML SQL statement, ability to identify results

Ability to use SQL to SELECT data from tablesAbility to use SQL to SELECT data from tables

Ability to use SQL to SORT or GROUP dataAbility to use SQL to SORT or GROUP data

Ability to use SQL to INSERT, UPDATE, or DELETE dataAbility to use SQL to INSERT, UPDATE, or DELETE data

Knowledge of transactions (i.e., COMMIT, ROLLBACK,Knowledge of transactions (i.e., COMMIT, ROLLBACK,

and transaction boundaries)and transaction boundaries)

Ability to call a procedure or invoke a user definedAbility to call a procedure or invoke a user defined

functionfunction

Given an XQuery statement, knowledge to identify resultsGiven an XQuery statement, knowledge to identify results

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What is (Structured Query Language) SQL?

Standard language of relational database access is SQL.Designed to access tabular data.

Invented by IBM in the 1970s, the SQL language continues toevolve and is the only way to access relational database data.

Three major categories.

- DDL (Data Definition Language) - Used to create, modify,or drop database objects

- DML (Data Manipulation Language) - Used to select, insert,update, or delete database data (records)

- DCL (Data Control Language) - Used to provide data objectaccess control

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Managing Database Objects - DDL

To create, modify, delete objects in a database, SQL DataDefinition Language (DDL) is used.

DDL has four basic SQL statements:

- CREATE

To create objects in a database.

- DECLARE

To create Temporary Tables in a database.

- ALTER

To make permitted alteration in structure of an object.

- DROP

To remove any object created with CREATE/ DECLAREstatements from database.


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Manipulate Data - DML

To retrieve, insert, update or delete from tables and/or views,SQL Data Manipulation Language (DML) is used.

DML also has four basic SQL statements:

- SELECT

To retrieve data from table or view.

- INSERT

To add records in tables.

- UPDATE

To change data.

- DELETE

To delete records from tables.

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Using SELECT to Retrieve Data

The SELECT statement is used to retrieve table orview data.

Syntax -

- SELECT [DISTINCT] columns

- FROM TABLE(S)

- WHERE condition

- GROUP BY column

- HAVING condition

- ORDER BY column

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Examples -

SELECT * FROM staff;

SELECT * FROM staff

FETCH FIRST 10 ROWS ONLY;

SELECT name, salary

FROM staff;

SELECT DISTINCT dept, job

FROM staff;

SELECT name, salary + comm AS pay

FROM staff;

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Question For You

Given the following Query:

SELECT last_name, first_name, age, hire_date

FROM employee WHERE age > 40

What will be the command:

To return the rows sorted by AGE, oldest first, and by

LAST_NAME, from A to Z

Answer: ORDER BY age DESC, last_name


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CASE Expressions In SELECT

SELECT empno, lastname, job, salary,

CASE WHEN job IN ('MANAGER, ADMIN)

THEN salary * 1.10

WHEN job IN ('DBA, ARCHITECT)

THEN salary * 1.08

WHEN job = 'PROGRAMMER'

THEN salary * 1.05

ELSE salary * 1.035

END as new_salary

FROM employee

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ExampleSELECT quantity,CASE WHEN itemcode = '099' THEN 'SILVER'WHEN itemcode = '788' THEN 'GOLD'WHEN itemcode = '899' THEN 'PLATINUM'ELSE 'ERROR'ENDFROM supplier

Query:SUPPLIER------------------------------------------QUANTITY ITEMCODE

3 0994 0991 7881 899

5 0093 7881 899

Output3,SILVER4,SILVER

1,PLATINUM1,ERROR5,SILVER3,GOLD

1,PLATINUM

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With WHERE clause

Use the WHERE clause to select specific rows from a table or

view.

Relational operators including:

=, >, =,


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Using Set Operators to Combine Multiple Queries

With DB2, it is possible to combine two or more queries into asingle query by using a special operator known as a setoperator. When a set operator is used, the results of eachquery executed are combined in a specific manner to producea single result data set

UNION - the result data sets produced by each individual queryare combined and all duplicate rows are eliminated

INTERSECT - common records that are found in both the result

data sets will be shown as final result set.EXCEPT - all records found in the first result data set that do

not have a corresponding record in the second result data setwill be shown as final result set.

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SELECT lastname, hiredate FROM employee

WHEREMONTHNAME(hiredate) = 'December' AND

salaryNOT BETWEEN 20000.00 AND 90000.00

SELECT * FROM emp_exp_02 UNION

SELECT * FROM emp_exp_01

SELECT empno, lastname FROM employee

WHERE lastname LIKE 'S%' ORDER BY empno

SELECT COUNT(*) FROM employee WHERE

workdept IN (SELECT deptno FROM department

WHERE admrdept = 'A00')

SELECT workdept, DECIMAL(AVG(salary), 9, 2)

AS avg_salary FROM employee GROUP BY work

dept HAVINGAVG(salary) > 60000

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Using Joins - Concepts

A join combines data from two or more tables. A joincondition is required to refine the result set (eliminates acartesian product). Joining can be INNER or OUTER.

INNER JOIN - Keeps only the rows from the cross productthat meet the join condition. If a row exists in both the tablesthen only they will be included in the result set.

OUTER JOIN is a concatenation of the inner join and rowsfrom the left table, right table, or both tables that are missingfrom the inner join. There are 3 types of Outer Join.

1. Left outer join = inner join + rows from the left table

2. Right outer join = inner join + rows from the right table

3. Full outer join = inner join + the rows from both the tables

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Using Joins Examples

SELECT lastname, deptname FROM employee e,

department d WHERE e.workdept = d.deptno

OR

SELECT lastname, deptname FROM employee e INNER

JOIN department d ON e.workdept = d.deptnoSELECT lastname, deptname FROM employee e LEFT

OUTER JOIN department d ON e.workdept = d.deptno

SELECT lastname, deptname FROM employee e RIGHT


SELECT lastname, deptname FROM employee e FULL



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INSERT Statement

The INSERT statement is used to add new rows to atable or a view.

Examples:

INSERT INTO staff VALUES

(1212,'Cerny',NULL,'Sales',3)

INSERT INTO staff (id, name, dept, job, years)

VALUES (1212,'Cerny',20,'Sales',3),

(1213,'Wolfrum',20,NULL,2)

INSERT INTO department (deptno, deptname)

SELECT deptno, deptname FROM sales_depts

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Example of inserting values in Table using

values of other Table Given the following two tables:

TAB1

C1 C2 __ __________1 Antarctica

2 Africa3 Asia4 Australia

TAB2

CX CY---- ---------5 Europe

6 North America7 South America

Query:Insert all rows found in table TAB2into table TAB1.

Command:INSERT INTO tab1 SELECT cx, cy

FROM tab2

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UPDATE Statement

The UPDATE statement is used to change the data in

a table or a view.

For example:

UPDATE staff SET dept = NULL

WHERE ename LIKE A%

UPDATE staff SET (dept, sal)=(51, 7000)

WHERE id = 750

UPDATE employees SET (dept) =

(SELECT deptname FROM department

WHERE deptno = 1)

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DELETE Statement

The DELETE statement is used to delete entire rows

of data from a table.

For example:

DELETE FROM staff WHERE id IN (1212, 1213)

DELETE FROM sales WHERE salesperson IS NULL


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The COMMIT and ROLLBACK statements

A unit of work (UOW), also known as a transaction, is arecoverablesequence of operations within an applicationprocess. Ex. transfer funds transaction.

The application ends the UOW by issuing either a COMMIT ora ROLLBACK statement, whichever is appropriate.

The COMMIT statement makes all changes made within the

UOW permanent, whereas the ROLLBACK statement reversesthose changes.

If the application ends normally without an explicit COMMIT orROLLBACK statement, the UOW is automatically committed.

If the application ends abnormally before the end of a UOW,that unit of work is automatically rolled back.

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Savepoints

A savepoint lets you selectively roll back a subset of actions

that make up a UOW without losing the entire transaction.

do some work;

savepoint A;

do some more work;

savepoint B;

do even more work;

savepoint C;

wrap it up;

roll back to savepoint B;

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Invoking User-Defined Functions

CREATE FUNCTION jobemployees (job VARCHAR(8))

RETURNS TABLE (empno CHAR(6),

firstname VARCHAR(12), lastname VARCHAR(15))

LANGUAGE SQL READS SQL DATA

NO EXTERNAL ACTION DETERMINISTICRETURN SELECT empno, firstnme, lastname

FROM employee

WHERE employee.job = jobemployees.job;

Calling function -

SELECT * FROM TABLE (jobemployees('CLERK'))

SELECT temp AS tempf, convert_temp(temp, 'F') AS tempcFROM climate_info


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Calling a Stored Procedure

CREATE PROCEDURE get_sales(IN quota INTEGER, OUT retcode CHAR(5))DYNAMIC RESULT SETS 1 LANGUAGE SQL

BEGIN

DECLARE sqlstate CHAR(5);DECLARE sales_results CURSOR WITH RETURN FORSELECT sales_person, SUM(sales) AS total_sales

FROM sales GROUP BY sales_personHAVING SUM(sales) > quota;

DECLARE EXIT HANDLER FOR SQLEXCEPTIONSET retcode = sqlstate; OPEN sales_results;SET retcode = sqlstate;

END

CALL get_sales (25, ?)

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What is XML?

XML was designed to structure, store and to senddata/information.

At its core XML is text formatted in the form of tags and textthat follow a well-defined set of rules.

This text may be stored/represented in:

- A normal file stored on disk

- A message being sent over HTTP

- A character string in a programming language

-A CLOB (character large object) in a database

- Any other way textual data can be used

John Smith Co

1234 W. Main StToledoOH95141

A5412

9851

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XML specifications

XMLdocument

s

XSD

XQuery XPathXSLT

DTDdescribes

describes

searches searches transforms

uses

uses

uses

uses

supersedes

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XPath Expressions

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XML Facilities XML data type for columns

-create s1.t1 (c1 int, c2 xml)

Language bindings for XML type in programming languages

- cobol, c, java, etc..

XML indexes

- create ix1 on s1.t1(c2) generate keys using pattern /dept/emp/@empno

An XML schema/DTD repository

Support for XQuery as a primary language as well as:

- Support for SQL within XQuery

-Support for XQuery with SQL

- Support for new SQL/XML functions

Performance, scale, and everything else they expect from a

DBMS

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Two ways to query XML data in DB2

Using XQuery as the primary language

- All queries begin with XQuery.

- Tells the DB2 parser what to expect

-Can execute SQL within a query beginning with XQUERY

Using SQL as the primary language

- Part 2

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XQuery: The FLWOR Expression

FOR: iterates through a sequence, bind variable to items LET: binds a variable to a sequence WHERE: eliminates items of the iteration ORDER: reorders items of the iteration RETURN: constructs query results

create table dept(deptID char(8), deptdoc xml);

xquery

for $d in db2-fn:xmlcolumn(dept.deptdoc)/dept

let $emp := $d//employee/name

where $d/@bldg > 95

order by $d/@bldg

return

{$d/@bldg, $emp}

John Doe

408 555 1212

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Peter Pan

408 555 9918

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Input:


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John DoePeter Pan

John DoePeter Pan

FLWOR Expression

John DoePeter Pan

xquery

for $d in xmlcolumn(deptdoc)/dept

where $d/@bldg = 101

return

{$d/employee/name}

This result is not an XML document!

xquery


where $d/@bldg = 101return $d/employee/name/text()

xquery


where $d/@bldg = 101

return $d/employee/name

John Doe

408 555 1212

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Peter Pan

408 555 9918

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create table dept (deptID char(8), deptdoc xml);

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Two ways to query XML data in DB2

Using XQuery as the primary language- Done

Using SQL as the primary language

- Looking at query only

- All queries begin with Select

- XML Retrieval done with XMLQUERY (flags db2 parser to

switch to XML Processing)

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XML Functions

XMLQUERY(). function that enables you to execute an XQueryexpression from within an SQL context. It returns an XMLvalue, which is an XML sequence. This sequence can beempty or it can contain one or more items.

XMLTABLE(). returns a table from the evaluation of XQueryexpressions; XQuery expressions normally return values as asequence, however, XMLTABLE() allows you to execute anXQuery expression and return values as a table instead.

XMLEXISTS(). If it returns an empty sequence, XMLEXISTSreturns FALSE; otherwise, TRUE is returned. The XMLEXISTSpredicate can be used in the WHERE clauses of UPDATE,DELETE, and SELECT statements.

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DML statements for XML Data

INSERT INTO customers (custinfo) VALUES (

XMLPARSE(DOCUMENT 'John Doe'PRESERVE WHITESPACE))

DELETE FROM customer WHERE XMLEXISTS ('declare

default element namespace "http://custrecord.dat";$info/customerinfo[name/text()=" John Doe"]'

PASSING custinfo AS "info")

UPDATE customerSET custinfo = XMLPARSE (DOCUMENT Jane

Doe PRESERVE WHITESPACE)WHERE empno = 11;


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XMLTABLE - XML to relational

95023USnull4711

33129USBobby1325

ZipZipTypeNameCID

SELECT X.* fromXMLTABLE (db2-fn:xmlcolumn(PORDERS.PO)//customerCOLUMNSCID INTEGER PATH @id,Name VARCHAR(30) PATH name,ZipType CHAR(2) PATH zip/@type,Zip XML PATH zip) AS X

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Given the following queries:

SELECT c1 FROM tab1; SELECT c1 FROM tab2;

Which of the following set operators can be used to

produce a result data set that contains only records

that are not found in the result data set produced by

each query after duplicate rows have beeneliminated?

A. UNION

B. INTERSECT

C. EXCEPT

D. MERGE

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Given the following UPDATE statement:

UPDATE employees SET workdept = (SELECT deptno FROMdepartment WHERE deptno = 'A01') WHERE workdept IS NULL

Which of the following describes the result if this statement is

executed?

A. The statement will fail because an UPDATE statement cannot

contain a subquery. B. The statement will only succeed if the data retrieved by the

subquery does not contain multiple records.

C. The statement will succeed; if the data retrieved by the subquery

contains multiple records, only the first record will be used to perform

the update.

D. The statement will only succeed if every record in theEMPLOYEES table has a null value in the WORKDEPT column.


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A stored procedure has been created with the

following statement:CREATE PROCEDURE proc1 (INvar1 VARCHAR(10), OUT rc INTEGER) SPECIFICmyproc LANGUAGE SQL What is the correct way

to invoke this procedure from the command line

processor (CLP)?

A. CALL proc1 ('SALES', ?)

B. CALL myproc ('SALES', ?)

C. CALL proc1 (SALES, ?)D. RUN proc1 (SALES, ?)

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