Database resources Link

Few gems on internet on the database concepts:

• http://www.eternallyconfuzzled.com/tuts/datastructures/jsw_tut_bst1.aspx

Hashing is such an important concept to understand,I find this very good.

• http://research.cs.vt.edu/AVresearch/hashing/buckethash.php

Database

While studying database course(RDBMS) in college I never thought I would end up doing database administration.At that time what we ever thought was doing coding and programming .However I was more into Discrete Mathematics and Data Structure and Operating System rather than Programming languages.
Though I liked the small book called "The Programming in C" by Dennis Ritchie. Its short and sweet.And believe me,it's very very powerful and concise.I never fully leverage it to become a good programmer but I think It can help whosoever wants to be a good programmer.
Now since I m now concerned with database so I would focus on database part.
Back in college days I barely realized that OS ,Data Structure and database are so intimately related but now I realize it do so. They are close kin.And I endorse the fact that theory plays as important role in understanding database as the hands on.
Those times, I had no real exposure to any DBMS apart from few times I played with MS SQL server.Now I work on IBM DB2 so got to know the practical aspect of database course.At that time I thought SQL is such an easy part for DBMS course all we needed to do was few SQL statements like "select *  from ".
But now it seems the whole world out there to understand. There are hordes of books available on this subject and many resources on internet, just Google any topic and u have plethora of links and some are worth following too :-) Like I just Google  "Hash table" and I get a very good article on wikipedia :
http://en.wikipedia.org/wiki/Hash_table
In a daily life of a DBA a topic like hash table hardly figures but I think One must have deeper understanding of the underlying DBMS, no matter what vendor 's flavor u are working on.

Everything about DB2 tables

Two SQL based ways to get detailed information on a DB2 table:

For example, we may want to know how much disk space has been allocated for a particular table, or what state it is in. Should it be reorganized? Has the last load job finished loading data in to it and so on

First Method:
using ADMINTABINFO view is one

SELECT * FROM SYSIBMADM.ADMINTABINFO;

The query is returning about 29 columns and this is for every table in the database.


Second Method:
The other is a to use SYSPROC.ADMIN_GET_TAB_INFO_V95 table function.


It accepts table schema and table name as parameters and returns exactly the same information as the ADMINTABINFO view.


SELECT * FROM TABLE (SYSPROC.ADMIN_GET_TAB_INFO_V95('ADMINISTRATOR', 'SALES'));

some typical DB2 SQL Queries

how to select a random row with DB2: 

SELECT column, RAND() as IDX 
FROM table 
ORDER BY IDX FETCH FIRST 1 ROWS ONLY

DB2 Functions:

Two types of functions can be applied to data in a DB2 table using SQL:

column functions and scalar functions.

example of Column function:

SELECT SUM(SALARY)
FROM EMP
WHERE WORKDEPT = 'D21';

example of Scalar function:

SELECT DAYOFWEEK(HIREDATE)
FROM EMP
WHERE EMPNO = '000100'; 

SELECT CEILING(3.5), CEILING(3.1), CEILING(-3.1), CEILING(-3.5)
FROM FROM SYSIBM.SYSDUMMY1; 

db2 updates large number of records

Disable Logging while executing updates for large number of records:
alter table activate not logged initially;
update set column=value where ;

but with caution  :
take a backup of the table by exporting the table  before executing the above query . If anything goes wrong (that is if your transaction rolls back for any other reason) you will have to drop the table and loose all the data.
I have faced a problem when I didn't exercise caution and eventually I needed to restore the whole database which was such a pain in the neck!
Error message was like you cannot access the table as NOT Logged Initially disable the logging and when the query took longer than expected I killed the query and consequentially table was not accessible.

Deleting Duplicate records from a table

OLAP function can be very handy sometimes.
and you can read about it on a developerworks
here is the link
http://www.ibm.com/developerworks/data/library/techarticle/dm-0401kuznetsov/index.html

here is the query which I have used

create view del_tmp as select SNO,VEH_REGN_NO ,row_number() over(partition by veh_regn_no) as row# from DWH.DWH_REG;
select * from del_tmp where row#>1;
select * from DWH.DWH_REG;

select count(*) from del_tmp where row# >= 2;
delete from del_tmp where row# >= 2

db2 monitoring

db2 "update monitor switches using lock ON sort ON bufferpool ON uow ON table ON statement ON"
db2 "get snapshot for tablespaces|tables| on db db_name"

and to see which switches are active:
use
db2 "get dbm monitor switches"

Note:don't use double quotes while running the command from CLP

the following links provide good explanation for monitoring database:

http://space.itpub.net/?uid-47598-action-viewspace-itemid-330882

http://www.performancewiki.com/db2-event-monitors.html

http://it.toolbox.com/blogs/db2luw/using-the-snapshot-monitor-and-monitoring-via-sql-5631