1. Add columns
ALTER TABLE table_name ADD (column datatype [DEFAULT expr][,column datatype ...]);
For example:
Sql>alter TABLE emp01 ADD Eno number (4);
2. Modifying the column definition
For example:
Sql>alter TABLE emp01 MODIFY Job VARCHAR2 (15)
2 DEFAULT ' clerk '
3. Delete Columns
For example:
sql> ALTER TABLE emp01 DROP COLUMN dno;
4. Modify column names
For example:
Sql>alter TABLE emp01 RENAME COLUMN Eno to Empno;
5. Modify the table name
For example:
Sql>rename EMP01 to employee;
6. Add comments
For example:
Sql>comment on TABLE employee is ' storing employee information ';
Sql>comment on TABLE employee.name is ' description of employee name ';
7. Length of the field ()
For example:
Select t.* from Tp_area t where substr (t.area_id,0,2) = ' ' and Length (t.area_id) >2
Oracle modifies tables, adds columns, deletes columns, modifies columns
