Creating and managing tables with SQL statements in Oracle

naming Conventions for table and column names :
Must start with a letter
Must be between 1-30 characters
can only contain a-z,a-z,0-9,_,$,#
Cannot duplicate user-defined other objects
Cannot use Oracle's reserved words

Pre-created conditions:
CREATE Table Permissions

When you build a table, you must specify:
Table name
Column name, column data type, maximum length

Data type:
VARCHAR2 (size) variable length character type (maximum length 4000 characters)
char (size) fixed length character type (maximum 2000 characters)
Number (p,s) numeric type
Date type
Long variable large character type (max. 2G)
CLOG large character type (max. 4G)
Raw Bare binary data (maximum 2000 characters)
Long raw bare binary data (2G max)
Blob binary data, Max 4G
bfile External binaries, Max 4G

Type	Meaning	Storage description	Note
CHAR	Fixed-length strings	Maximum length 2000bytes
VARCHAR2	Variable-length strings ,	Maximum length 4000bytes	Maximum length of index can be made 749
NCHAR	Fixed-length strings based on character set	Maximum length 2000bytes
NVARCHAR2	Variable-length strings based on character set	Maximum length 4000bytes
DATE	Date (Day - month - year)	Dd-mm-yy (HH-MI-SS), after rigorous testing, no problem of thousand worms
TIMESTAMP	Date (Day - month - year)	Dd-mm-yy (HH-MI-SS:FF3), after rigorous testing, no problem of thousand worms	compared to DATE,TIMESTAMP has a decimal-seconds message
LONG	Super Long string	Maximum length 2G, enough to store tome
RAW	Fixed-length binary data	Maximum length 2000bytes	can store multimedia image sound, etc.
LONG RAW	Variable-length binary data	Maximum length 2G	can store multimedia image sound, etc.
Blob	Binary data	Maximum length 4G
Clob	Character data	Maximum length 4G
NCLOB	Character data based on the character set	Maximum length 4G
BFILE	Binary data stored outside the database	Maximum length 4G
ROWID	Unique line number recorded in the datasheet	10bytes	. ****.**** format,* is 0 or 1
Nrowid	Unique line number recorded in a Binary data table	Maximum length 4000bytes
Number (P,s)	Number Type	P is the integer digit,S is the decimal digit
DECIMAL (P,s)	Number Type	P is the integer digit,S is the decimal digit
INTEGER	Integer type	A small integer
FLOAT	Floating-point type	Number (+), double precision
REAL	Real type	Number (+), higher accuracy

Create syntax:
CREATE table [schema.] TableName
(column datatype [default expr] [Constaint],
....)

To view the table structure:
DESC TableName

Types of Oracle Tables
User-defined Tables
Data dictionary
A set of tables created automatically by Oracle
Contains the database's own information for managing and maintaining the database

About data dictionaries for tables:
User_catalog,all_catalog,dba_catalog,
User_tables,all_tables,dba_tables,

User_tables Self-built tables
All_tables Self-accessible tables
Dba_tables all tables in the database

How to clone a table
To clone an entire table:
CREATE TABLE EMP as SELECT * from Scott.emp;
Clone table Structure:
CREATE TABLE EMP2 as SELECT * from Scott.emp where 1=2;


How to view disk space consumed by a table:
Dba_extents,
Dba_segments

INSERT INTO EMP SELECT * from EMP;

Select Segment_name,sum (BYTES)/1024/1024
From dba_extents where segment_name= ' EMP ' and owner= ' SYS '
GROUP by Segment_name;

Selectowner,segment_name,segment_type,
tablespace_name,bytes/1024/1024
From dba_segments WHERE segment_name= ' EMP ';

Updating table information in a data dictionary
exec dbms_stats.gather_table_stats (' SCOTT ', ' TEST ');

To modify a table:
Add New Column
ALTER TABLE TableName
Add (column datatype [default expr]);

To delete a column:
ALTER TABLE TableName
Drop Column ColName

Column renaming:
ALTER TABLE TableName
Rename column colname to New_colname

Table renaming:
ALTER TABLE tablename Rename to New_tablename
Rename Test2 to test

Modify the data type, size, and default value of a column
ALTER TABLE TableName
Modify (column datatype [default values])

To mark a column as unavailable:
ALTER TABLE TableName
Set Unused (column)

Delete a table
DROP TABLE TableName

Truncate TABLE (delete all records, keep table structure)
TRUNCATE TABLE TableName

Table Plus comments
Comment on table tablename is ' ... Comment Content ... '

Column Plus Comment
Comment on column tablename.column is ' ... '

Data dictionaries related to annotations
All_col_comments
User_col_comments

All_tab_comments
User_tab_comments

Data dictionary about the table structure:
Dba_tab_columns

Using null values and default values
Implicit: Do not specify a field when inserting a record, do not specify a value
Display: Empty value field is null when inserting record, default field is filled

Reference: http://blog.sina.com.cn/s/blog_690d63f80100jiq4.html

Creating and managing tables with SQL statements in Oracle