Term: ALTER

Definition:
The Oracle ALTER statement allows you to make changes to an existing table. It is also used to add, modify, or drop a column from an existing table. The basic syntax for renaming a table is:

ALTER TABLE table_old_name

RENAME TO table_new_name;

To add a column to a table, the syntax is:

ALTER TABLE table_name

ADD column_name column-definition;

For example:

ALTER TABLE users

 ADD user_name  varchar2(50);

You may add multiple columns with a single ALTER statement. Each column must have its own definition.

The ALTER TABLE syntax to DROP a column is:

ALTER TABLE table_name

DROP COLUMN column_name;

For example:

ALTER TABLE users

DROP COLUMN user_name;

In Oracle 9i and above, you can use the ALTER statement along with the RENAME statement to change the name of a table column. Example syntax is shown here:

ALTER TABLE users

RENAME COLUMN first_name TO  user_first_name;

Related Links:

Oracle Tables: ALTER Examples & Syntax

Related Code Snippets:

Alter Table - Example of altering the datatypes or lengths of fields in the table.
USERS: Alter a user - Change a user's password.
INDEXES: Alter index - Example of altering an index (rename, collect statistics, etc).
PACKAGES: alter package
INDEXES: Alter Index Allocate Extent - Use the ALTER INDEX statement to change or rebuild an exist...
INDEXES: Alter Index Deallocate Unused - Use the deallocate_unused_clause to explicitly deallocate...
INDEXES: Alter Index Parallel - Use the PARALLEL clause to change the default degree of parallelis...
TABLESPACE: Alter Permanent Tablespace - Various examples of manipulating permanent tablespace set...