Data
definition language is a sub language of sql respond able to create and
manipulate table structure in oracle to do so DDL provide following statement
1.
Create
2.
Alter
3.
Drop
4.
Truncate
5.
Rename
Syntax of create a table
Create table <t_name>
( col_name datatype(size),
Col_name datatype(size),
Col_name datatype(size)
................ n );
Ex
Create
table sysemp
(empno
number(4), name varchar2(10), sal number(7,2));
The
above ex create a table structure physical in oracle data base
NOTE:
Once table structure is created to
display the structure of table user can use describe, desc command
SQL> desc
sysemp
Modification
using Alter:
Alter
of table means
è Add
after new column after table design
è Deleting
of exiting column
è Changing
a data type of column
è Changing
the size of table
Add and Modifies:
Alter table
<t_name>
Add/Modify
(c_name datatype(size), col_name datatype(size)..................N);
NOTE :
To add a new column, to delete a exiting
column or change size of column is possible weather table not contain the data
but change the data type of column a column must be empty.
Syntax to delete and exiting column:
Alter table<t_name>
Drop
<col_name>
Above
command is required to delete single column from exiting column
Alter
table<t_name>
Drop (col1,
col2, col3.....N);
Above
column required to delete multiple columns.
Ex
1)
Alter table sysemp
Drop
job;
2)
Alter table sysemp
Drop
job,name;
NOTE:
“User can not be
delete all column of table using alter.”
Deleting table structure using drop
Drop
table <t_name>;
Ex
Drop
table sysemp;
Above
example will delete structure as well as data of a table.
Deleting
all records of table physical remaining the structure using truncate.
TRUCATE TABLE <T_NAME>;
Ex
Truncate
table sysemp;
Rename a table using rename
RENAME
<T1_NAME> TO <T2_NAME>;
Ex
Rename
sysemp to sysemp2;
