Base De Datoss

Renaming a table
The basic syntax for renaming a table is:
ALTER TABLE table_name
 RENAME TO new_table_name;
For example:
ALTER TABLE suppliers
 RENAME TO vendors;
This will renamethe suppliers table to vendors.

Adding column(s) to a table
Syntax #1
To add a column to an existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name
 ADD column_name column-definition;
Forexample:
ALTER TABLE supplier
 ADD supplier_name  varchar2(50);
This will add a column called supplier_name to the supplier table.

Syntax #2
To add multiple columns to an existing table, the ALTERTABLE syntax is:
ALTER TABLE table_name |
ADD ( | column_1 | column-definition, |
  | column_2 | column-definition, |
  | ... | |
  | column_n | column_definition ); |
For example:
ALTERTABLE supplier |
ADD ( | supplier_name | varchar2(50), |
  | city | varchar2(45) ); |
This will add two columns (supplier_name and city) to the supplier table.

Modifying column(s) in a tableSyntax #1
To modify a column in an existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name
 MODIFY column_name column_type;
For example:
ALTER TABLE supplier
 MODIFY supplier_name  varchar2(100)     not null;
This will modify the column called supplier_name to be a data type of varchar2(100) and force the column to not allow null values.

Syntax #2
To modify multiple columns inan existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name |
MODIFY ( | column_1 | column_type, |
  | column_2 | column_type, |
  | ... | |
  | column_n | column_type ); |
Forexample:
ALTER TABLE supplier |
MODIFY ( | supplier_name | varchar2(100) | not null, |
| city | varchar2(75) |   | ); |
This will modify both the supplier_name and city columns.

Dropcolumn(s) in a table
Syntax #1
To drop a column in an existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name
 DROP COLUMN column_name;
For example:
ALTER TABLE supplier
 DROP COLUMN...