I will temporary transmit this blog to http://miloluo.blog.chinaunix.net

Pls kindly known that.

Milo.

No mater how hard we have been though and are being thought...
No mater what kinds of situations our family meets...
No mater how other people thinks...

I will always do what should be in my dreams...
I will try all my energies to solve problems...
I will ingore all prejudices...

Anyway, all the fires and all the courages will penetrate all my life!

The nine year's old boy named Lin Hao.He was at classroom when the big earthquake occured on PM 2:28 ,May 12,2008.His teacher told him and his classmates to run outside.While running outside,the boy found his two classmates fainted on the half way. The boy turned round immediate and carried his two classmates on his back and shoulder without hesitate.Because of these action,he got hurt on his arms. And the boy and his little sister and elder sister walked from Yin Xiu town to Du Jiangyan city,but he still have got any news about his parents. This little boy  impressed  me as brave ,kind-hearted and iron will.
Hope all his families all good !

Let us pray for all the people in this big disaster !
Let us thank those people for rescuing people and curing people that hurted　！
Let us be a family !
                   
                                                              Milo Luo
                                                                       May 21 2008

Here are some codes , i wrote in Eric's Assignments.

• The first one is used for caculating the area of circle.

DECLARE
   R NUMBER := &radius;
   PI CONSTANT NUMBER  := 3.14;
BEGIN
   DBMS_OUTPUT.PUT_LINE('The area of the circle is ' || PI * R * R );
END;
/

These is another way to do it:
DECLARE
       r NUMBER(5,2);
       PI CONSTANT number(5,2) := 3.1415;
BEGIN
       DBMS_OUTPUT.put_line('The area of circle is : ' || PI * power(&r,2) );
END;

I dont know which is more faster.May be it's too small calculation for cpu or for oracle software.I did some experiences and it haven't show me the very differeces.

SQL> DECLARE
  2         r NUMBER(5,2);
  3         PI CONSTANT number(5,2) := 3.1415;
  4  BEGIN
  5         DBMS_OUTPUT.put_line('The area of circle is : ' || PI * power(&r,2) );
  6  END;
  7  /
Enter value for r: 3.14
The area of circle is : 30.959144

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.00
SQL> DECLARE
  2     R NUMBER := &radius;
  3     PI CONSTANT NUMBER  := 3.14;
  4  BEGIN
  5     DBMS_OUTPUT.PUT_LINE('The area of the circle is ' || PI * R * R );
  6  END;
  7  /
Enter value for radius: 3.14
The area of the circle is 30.959144

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.00
SQL> /
Enter value for radius: 3.1415926536987932384626433832795028841971693993
The area of the circle is 30.99055782157106906641289334720356321367

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.00

Here we introduce some basic skill of PL/SQL and its tools.

First,I wanna introduce settings we wanna set before we coding.
1.set serveroutput on
2.set verify off

Second,You should keep your code styles more readable.

If you want your output pretty neat,you should follow this rules:
Oracle KEY WORDS should in UPCASE,such as DECLARE,BEGIN,END,IF and so on.
Here is a example：

/*              Author: Milo       Date: April,16th ,2008        Specification:A script to calculate circle area.*/DECLARE          R NUMBER := &radius;   PI CONSTANT NUMBER  := 3.14;BEGIN      DBMS_OUTPUT.PUT_LINE('The area of the circle is ' || PI * R * R );END;/


And also try to put some commends when necessary.


Third,We can use only three ways to assign values to pl/sql variable:


Assigning Values to VariablesYou can use assignment statements to assign values to variables. For example, thefollowing statement assigns a new value to the variable bonus, overwriting its oldvalue:bonus := salary * 0.15;


Variables and constants are initialized every time a block or subprogram is entered. Bydefault, variables are initialized to NULL. Unless you expressly initialize a variable, itsvalue is undefined (NULL) as shown in Example 2–20.Example 2–20 Initialization of Variables and ConstantsDECLAREcounter INTEGER;BEGIN-- COUNTER is initially NULL, so 'COUNTER + 1' is also null.counter := counter + 1;IF counter IS NULL THENDBMS_OUTPUT.PUT_LINE('COUNTER is NULL not 1.');END IF;END;/To avoid unexpected results, never reference a variable before you assign it a value.The expression following the assignment operator can be arbitrarily complex, but itmust yield a datatype that is the same as or convertible to the datatype of the variable.PL/SQL Expressions and ComparisonsFundamentals of the PL/SQL Language 2-19


Assigning BOOLEAN ValuesOnly the values TRUE, FALSE, and NULL can be assigned to a BOOLEAN variable asshown in Example 2–21. You can assign these literal values, or expressions such ascomparisons using relational operators.Example 2–21 Assigning BOOLEAN ValuesDECLAREdone BOOLEAN; -- DONE is initially NULLcounter NUMBER := 0;BEGINdone := FALSE; -- Assign a literal valueWHILE done != TRUE -- Compare to a literal valueLOOPcounter := counter + 1;done := (counter > 500); -- If counter > 500, DONE = TRUEEND LOOP;END;/


Assigning a SQL Query Result to a PL/SQL VariableYou can use the SELECT statement to have Oracle assign values to a variable. For eachitem in the select list, there must be a corresponding, type-compatible variable in theINTO list as shown in Example 2–22.Example 2–22 Assigning a Query Result to a VariableDECLAREemp_id employees.employee_id%TYPE := 100;emp_name employees.last_name%TYPE;wages NUMBER(7,2);BEGINSELECT last_name, salary + (salary * nvl(commission_pct,0))INTO emp_name, wages FROM employeesWHERE employee_id = emp_id;DBMS_OUTPUT.PUT_LINE('Employee ' || emp_name || ' might make ' || wages);END;/Because SQL does not have a BOOLEAN type, you cannot select column values into aBOOLEAN variable. For additional information on assigning variables with the DMLstatements, including situations when the value of a variable is undefined.

Enter user-name: system
Enter password: ********

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options

SQL> conn milo/milo;
Connected.
SQL> create tablespace milo;
create tablespace milo
                     *
ERROR at line 1:
ORA-02199: missing DATAFILE/TEMPFILE clause

SQL> create tablespace milo datafile '/home/milo/datafile/milo.dbf'
  2  size  10M;
create tablespace milo datafile '/home/milo/datafile/milo.dbf'
*
ERROR at line 1:
ORA-01119: error in creating database file '/home/milo/datafile/milo.dbf'
ORA-27037: unable to obtain file status
Linux Error: 13: Permission denied
Additional information: 1

SQL> select tablespace_name,file_name from dba_data_files;

TABLESPACE_NAME
------------------------------
FILE_NAME
--------------------------------------------------------------------------------
USERS
/u01/app/oracle/oradata/LOVEU/users01.dbf

SYSAUX
/u01/app/oracle/oradata/LOVEU/sysaux01.dbf

UNDOTBS1
/u01/app/oracle/oradata/LOVEU/undotbs01.dbf

TABLESPACE_NAME
------------------------------
FILE_NAME
--------------------------------------------------------------------------------
SYSTEM
/u01/app/oracle/oradata/LOVEU/system01.dbf

SQL> create tablespace milo '/u01/app/oracle/oradata/LOVEU/milo.dbf' size 10M;
create tablespace milo '/u01/app/oracle/oradata/LOVEU/milo.dbf' size 10M
                       *
ERROR at line 1:
ORA-02180: invalid option for CREATE TABLESPACE

SQL> create tablespace milo datafile '/u01/app/oracle/oradata/LOVEU/milo.dbf' size 10M;

Tablespace created.

SQL> create tablespace snowball datafile '/home/oracle/snowball.dbf' size 10M;
Tablespace created.

SQL> alter user milo default tablespace milo;

User altered.