What are “%1” and “%2” in batch files?

It represents the first command line argument passed to the batch file.
If you run your batch file with:

myfile.bat firstArg secondArg

%1 becomes “firstArg” and %2 becomes “secondArg”
The related shift command shifts the position of arguments one to the left. Running shift once in a batch file will make “%1” value to be the second argument, “%2” becomes the third, and so on. It’s useful for processing command line arguments in a loop in the batch file.

http://stackoverflow.com/questions/2309968/what-are-1-and-2-in-batch-files

How to run this java class in command line in windows?

You would run

java com.test01.test01

but having a class with the same name as a package is a really bad idea (as well as not following the Java naming conventions).
You’d need to run it with the relevant class on the classpath. For example, you could just compile it like this (from the “root” of your source tree):

javac -d . [path to source file]
java com.test01.test01

or if you’ve got your source organized appropriately already:

javac com\test01\test01.java
java com.test01.test01

http://stackoverflow.com/questions/6314648/how-to-run-this-java-class-in-command-line-in-windows

Changing current version of Java within Windows

In the command shell:

set JAVA_HOME=C:\jdk1.6.0u24
set PATH=%JAVA_HOME%\bin;%PATH%

That will temporarily set up the environment in the command shell. Maven, Ant, etc. will pick up on your new version of Java without having to go to the Control Panel repeatedly.
Tools like Eclipse should be able to select which JDK to use in their own configuration tools for use within their environments.

http://superuser.com/questions/262757/changing-current-version-of-java-within-windows

What is the dual table in Oracle?

It’s a sort of dummy table with a single record used for selecting when you’re not actually interested in the data, but instead want the results of some system function in a select statement:
e.g. select sysdate from dual;
See http://www.adp-gmbh.ch/ora/misc/dual.html

http://stackoverflow.com/questions/73751/what-is-the-dual-table-in-oracle

ora-00979 not a GROUP BY expression

You must put all columns of the SELECT in the GROUP BY or use functions on them which compress the results to a single value (like MIN, MAX or SUM).

http://stackoverflow.com/questions/1520608/ora-00979-not-a-group-by-expression