DB2 uses a dictionary based algorithm for compressing data records. DB2 9 will scan tables, and search for duplicate occurrences, then assign a short numeric key to each entries. You will understand better with a picture:

Compress data

Each new occurences of “Sophie”, “New York”, “IBM US”, will be respectively assign to “(01)”, “(19)” and “(09)”. This is very useful on large table. Each time a new row is added to the table, DB2 will automatically compress these new data.

Seems to be good, let’s try on our DB2 now. To enable the compression,  we should turn on the “COMPRESS” option on the table.

CREATE TABLE Users COMPRESS YES

or use alter if the table is already created:

ALTER TABLE Users COMPRESS YES

Typically, we can save an average ratio of 45 to 75 percent of our storage space. Next time, we’ll see how to use the inspect tool, to determine the compression ratio.

To define this variable, let’s use the DB2set command:

Db2set DB2_CLPPROMPT="db2isgreat> "

Our new DB2 Prompt will be “db2isgreat> “. It’s much more better, but we can do more. DB2_CLPPROMPT registry variable can contain the tokens %n, %ia, %d, %da and %i:

• %n – New line
• %ia – Authorization ID of the current instance attachment
• %d – Local alias of the currently connected database
• %da – Authorization ID of the current database connection
• %i – Local alias of the currently attached instance

Now, let’s try with these tokens:

Db2set DB2_CLPPROMPT="%ia@%i, %da@%d> "

With an instance attachment to instance “DB2″ with authorization ID “mycado”. Database “sample” with authorization ID “mycadoax”, will return something like:

MYCADO@DB2, MYCADOAX@SAMPLE >

You can now everytime where you are, and one which instance/database you’re working on.

And also, some useful mapping between Oracle and DB2 products:

You should also take care of the “package” term. For Oracle it’s a logical grouping of PL/SQL blocks that can be invoked by other PL/SQL applications, and for DB2 it’s a precompiled access plan for an embedded static SQL application stored in the server.

For the SQL query, nothing more than a SELECT:

SELECT id, info from client

Easy, but not really powerful for XML data, let’s try with XQuery, who give us two functions for DB2. db2-fn:sqlquery and db2-fn:xmlcolumn. The first function retrieves a sequence that is the result of an SQL fullselect and the second retrieves a sequence from a column. One important thing you should keep in mind, SQL is not a case-sensitive language alors que XQuery is a case-sensitive language.

An example which return all the XML data from the “info” column:

XQUERY db2-fnxmlcolumn ('CLIENT.INFO')

Which is same as this SQL query:

SELECT info FROM client

Let’s see something more nice. This query will return all the elements in <name> , inside the “info” column, and with the <city> element which containt “Paris”:

XQUERY declare defaut element namespace "http://posample.org";
for $d in db2-fn:xmlcolumn('CLIENT.INFO')/clientinfo
  where $d/addr/city="Paris"
return <out>{$d/name}</out>

db2-fn:xmlcolumn retrieves the data from the “info” column in the “client” table. We add a $d variable, for each element of <clientinfo>, and we use a where to filter the <city> element which should be “Paris. To finish, we use <out> to output the data:

<out xmlns="http://posample.org">
  <name>Sophie Bool</name>
</out>

XQUERY declare default element namespace "http://posample.org";
for $d in db2-fn:sqlquery('SELECT info FROM client')/clientinfo
  where $d/addr/city="Paris
return <out>{$d/name}</out>

So, it’s funny, but why it’s interesting to do that ? Because XML data are hierarchic (instead of relational data which are flat) and data self-describing through XML tags. XML also allows a better flexibility for data structures required to change very often. In the other hand, access time performances will be a little slower, we lose the integrity constraints, and OLAP queries will be more difficult. The important question is “Which flexibility-performance ratio do you need ?”.

Let’s start now with the creation of a database, which should be encoded with UTF-8, to store XML. For that, we use the CREATE DATABASE command:

CREATE DATABASE xmldb USING CODESET UTF-8 TERRITORY US

We have our table, now we should create the “client” table, with an “info” column who contain client information, in XML format:

CONNECT TO xmldb
CREATE TABLE client (id INT, info XML)

Let’s try to insert a new client with a SQL query:

INSERT INTO client (id, info) VALUES (1, '<clientinfo xmlns="http://posample.org" Cid="1"><name>Sophie Bool</name><addr country="France"><street>5 rue du chateau de stable</street><city>Paris</city></addr><phone type="work">01 72 92 02 88</phone></clientinfo>')

The first thing you will told me is this query is a normal SQL query, and this is right, insert XML isn’t more difficult. The second thing is about the XML, here we have a short XML data, but if we have more, it will be very difficult to use. This why, we will use XQuery to manipulate these data or use a XDS import. I’ll come back soon on these points.

The case study will explain:

• How the project was started
• Which techniques and strategy were used
• How follow-up was done
• What investments where made
• What was the return on investment

The speakers are Surekha Parekh, DB2 Market Manager/Strategist, IBM Software Group and Kurt Struyf, Senior Consultant from Competence Partners.

You can register at SQL tuning: the necessity, the benefits, a business case.

After the installation, we will use these functions as normal PHP functions. This is a connection example to the SAMPLE database. You can click on the function to get more information:

<?php
$conn = db2_connect('SAMPLE', 'db2user', 'secretpass');

if($conn) {
  echo "connection to sample: ok.";
} else {
  echo "connection to sample: failed.";
}

db2_close($conn);
?>

Nothing very complicated here, we connect to the SAMPLE database with the db2_connect function, and we check if the connection works, then we close the connection with db2_close.

Now, let’s do something more interesting, do some query on our tables !

<?php
$query = "SELECT * FROM ADMINISTRATOR.EMPLOYEE";
$stmt = db2_prepare($conn, $query);

if($stmt) {
  $ex = db2_execute($stmt);
  if($ex) {
    while($ligne = db2_fetch_array($stmt)) {
      $lastname = ligne[3];
      echo "<br />- $lastname";
    }
  }
}
?>

We put your query in the $query variable, and we use the db2_prepare function with the previous connection ($conn). This function will “prepare” (I’m so smart), it will create an optimized path in DB2, to be more fast. We execute this result ($stmt) with the db2_execute function, who do the query on your database. To finish, we use db2_fetch_array to retrieve our data in an array.

A BLOB example.. or Binary Large OBject, an image, a audio or video file,..

$filename = '/home/mycado/itsme.jpg';
$name = 'My cute picture";

$query = 'INSERT INTO photo (id, name, image) VALUES (?, ?, ?)';
$stmt = db2_prepare($conn, $query);

if($stmt) {
  db2_bind_param($stmt, 1, 'id', DB2_PARAM_IN);
  db2_bind_param($stmt, 2, 'name', DB2_PARAM_IN);
  db2_bind_param($stmt, 3, 'filename', DB2_PARAM_FILE);

  $ex = db2_execute($stmt);
}

We use the flag db2_bind_param we give us more precision with the data type in our request. The first two variables, an id and a string, use DB2_PARAM_IN, an classical input parameter et we put your picture with DB2_PARAM_FILE. Note that the question marks are not an error !

It’s enough for now, I advice you to read the ebook “DB2 Express-C: The Developer Handbook for XML, PHP, C/C++, Java, and .NET‘. About the ibm_db2 functions, you can find them all on php.net.

IBM DB2 is a relational database management system, using SQL language. Created in 1983 by IBM, and the last version is the 9.7 (Cobra). Compatible with the major operating systems (z/OS, AIX, Unix, Linux, Windows, Mac OS,..), DB2 ranks second in terms of market share, behind Oracle. There are several versions of DB2, more or less specialized and offer more or less services, but we will choose the free version, who can be use by students, developers, or small companies. DB2 Express-C is free to develop, deploy and distribute.

DB2 Express-C only have two limitations, which are not problem for us. It supports only 2 core and up to 2GB of RAM, which is enough for our tests. This version is available for Linux (32bit, 64bit and POWER), Windos (32bit and 64bit), Solaris (Intel 64bit), and Mac OS X (Intel 64bit), but unavailable for z/OS.. still not a problem for us ! There is no other limitation, we are free for the database size, number of connected users,.. Whether you develop in Java, .Net, Ruby, Python, Perl or pretty much any other programming language out there

We will proceed to the crucial stage, downloading DB2 Express-C 9.7 and install it on your system. To go further, don’t hesitate to consult the excellent ebook “Getting Started with DB2 Express-C” and watch the videos on channelDB2.

DXIIC:/ mycado$ db2level

DB221085I Instance “DB2″ uses “32″ bits and DB2 code release “SQL09052″ with level identifier “03030107″.
Informational tokens are “DB2 v9.5.200.315″, “s080811″, “WR21411″, and Fix Pack “2″.
Product is installed at “C:\DB2v95″ with DB2 Copy Name “DB2COPY1″.

Here I use a DB2 9.5 with the fix pack 2 ! These information can be useful when you search information or when you need a support from IBM, but essentially to know if you have the latest fixpack. The latest fixpack for DB2 9.5 is the fix pack 4.