ALTER

The ALTER TABLE command allows you to add, modify, or drop acolumn from an existing table.

Adding column(s) to a table

Syntax #1

To add a column to an existing table, the ALTER TABLE syntaxis:

ALTER TABLE table_name
ADD column_name column-definition;

For example:

ALTER TABLE supplier
ADD supplier_name varchar2(50);

This will add a column called supplier_name to thesupplier table.

Syntax #2

To add multiple columns to an existing table, the ALTER TABLEsyntax is:

ALTER TABLE table_name
ADD (	column_1	column-definition,
	column_2	column-definition,
	...
	column_n	column_definition );

For example:

ALTER TABLE supplier
ADD (	supplier_name	varchar2(50),
	city	varchar2(45) );

This will add two columns (supplier_name andcity) to the supplier table.

Modifying column(s) in a table

Syntax #1

To modify a column in an existing table, the ALTER TABLE syntaxis:

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 bea data type of varchar2(100) and force the column to not allow nullvalues.

Syntax #2

To modify multiple columns in an existing table, the ALTER TABLEsyntax is:

ALTER TABLE table_name
MODIFY (	column_1	column_type,
	column_2	column_type,
	...
	column_n	column_type );

For example:

ALTER TABLE supplier
MODIFY (	supplier_name	varchar2(100)	not null,
	city	varchar2(75)		);

This will modify both the supplier_name andcity columns.

Drop column(s) in a table

Syntax #1

To drop a column in an existing table, the ALTER TABLE syntaxis:

ALTER TABLE table_name
DROP COLUMN column_name;

For example:

ALTER TABLE supplier
DROP COLUMN supplier_name;

This will drop the column called supplier_name from thetable called supplier.

Rename column(s) in a table
(NEW in Oracle 9i Release 2)

Syntax #1

Starting in Oracle 9i Release 2, you can now rename acolumn.

To rename a column in an existing table, the ALTER TABLE syntaxis:

ALTER TABLE table_name
RENAME COLUMN old_name to new_name;

For example:

ALTER TABLE supplier
RENAME COLUMN supplier_name to sname;

This will rename the column called supplier_name tosname.