Thinking Of Mathematics

"The world is too full of factors to discourage students who cannot see from pursuing a career in science and math; hopefully this article can serve to at least minimally offset that imbalance."

- T. V. Raman

I was reading "Thinking Of Mathematics — An Essay On Eyes-free Computing" [ PDF version ] & found it inspiring. T. V. Raman's analysis of "Eyes-free mathematics" & his application of Herman Helmholtz's theories to attempt & understand his own creative thinking are excellent.

T.V Raman was unable to see since the age of 14. He narrates his thought process on problem solving, modeled on Herman Helmholtz's three stages of creativity: saturation, incubation and illumination. He shares his experiences on solving interesting problems like a Mental Calendar, Solving The Rubik’s Cube, etc.

The essay is truly a wonderful & inspiring read.

ORA-01940: cannot DROP a user that is currently logged in

" ORA-01940: cannot DROP a user that is currently logged in "

ORA-01940

We were trying to drop a user ( schema ) in our local Oracle Database & we suddenly hit the ORA-01940 error.

We closed all the SQL Clients ( Oracle SQL Developer, SQL* Plus, TOAD ) that we were using, but still the error persisted. We were quite flummoxed - until, we googled and landed on this article from Burleson Consulting.

We followed the advice in the article & quitely killed the "stale" sessions. We could then drop the schema and recreate it.

I have always admired the articles from Burleson Consulting & found the explanation of the ORA-01940 error very informative.

Groovy test ride

" Groovy is an agile and dynamic language for the Java Virtual Machine "

- Groovy Home Page

I have been following the Java scripting languages landscape for quite sometime now. I am simply overwhelmed with the sheer number of scriprting languages that can be run off the JVM. I was keenly following one such scripting language with interest - Groovy. I finally decided to take Groovy for a test ride, after reading a lot of interesting stuff on blogs & articles. I decided to try a simple example & see what I can learn from my experiment.

What's the Scenario ?

I have two database tables - EMP ( to keep details of employees ) and DEPT ( to keep details of departments ). I want to pull out details of an employee from the EMP ( Employee Number, Employee Name, Salary ) and DEPT ( Department Name ) tables and store it in another table named EMP_REPORT ( Employee Number, Employee Name, Salary, Department Name )

What am I going to use ?

• Microsoft Windows XP [Version 5.1]
• Java 1.5
• Groovy 1.5.4
• Oracle Database 10g Enterprise Edition Release 10.1.0.4.2
• Oracle SQL Developer 1.2.1

What are the logical steps ?

1. Connect : to the Database.
2. Query : the tables EMP and DEPT using a SQL SELECT statement.
3. Results : get the Result Ser
3. Iterate : the result set and get each record.
4. Add : each record to the EMP_RECORDS table.

What about installation ?

The installation procedure for Groovy is very easy - download & unzip. If you have set the JAVA_HOME environment variable to point to your JDK installation directory, you can just proceed to Groovy's /bin directory and double click on GroovyConsole.bat. You can see a simple IDE that allows you to execute your Groovy code. You can use CTRL + R to execute the code and CTRL+W to clear the output window.

... and...What does the Groovy code look like ?

import groovy.sql.Sql
import groovy.xml.MarkupBuilder

def source = Sql.newInstance(
"jdbc:oracle:thin:user/password@host:port:sid",
"oracle.jdbc.driver.OracleDriver"
)

def target = Sql.newInstance(
"jdbc:oracle:thin:user/password@host:port:sid",
"oracle.jdbc.driver.OracleDriver"
)

def sourceEmployees = source.dataSet("EMP E,DEPT D WHERE E.DEPTNO=D.DEPTNO")
def targetEmployees = target.dataSet("EMP_REPORT")

sourceEmployees.each
{
targetEmployees.add( ID : it.empno , NAME : it.ename , SAlARY : it.sal , DEPARTMENT : it.dname )
}

My thoughts ?

Well, that was quite easy ! It took less that 10 minutes for me to setup Groovy & try the code. I only faced one problem - Groovy complained that it couldn't find the Database Driver class oracle.jdbc.driver.OracleDriver. I simply put ojdbc14.jar into my JAVA_HOME/jre/ext/lib folder as a workaround.

I found Groovy to be simple & much closer to Java than the other scripting languages touted for the JVM. I think I'll probably use it for prototyping something in Java/JEE in the future.