The SQL ALTER TABLE statement is used to add, modify, or drop columns in a table.
The general format is:
ALTER TABLE [schema.]tablename {ADD|MODIFY|DROP}...
Example 1, rename a table:
ALTER TABLE tablename RENAME TO newtablename;
Example 2, add column:
ALTER TABLE invoice ADD detailname varchar2(50);
Example 3, modify column:
ALTER TABLE invoice MODIFY detailname varchar2(50);
ALTER TABLE invoice MODIFY detailname NOT NULL;
Example 4, drop column:
ALTER TABLE invoice DROP COLUMN detailname;
Example 5, rename column:
ALTER TABLE invoice RENAME COLUMN detailname TO longname;
Example 6, default value:
ALTER TABLE invoice MODIFY detailname Varchar2(135) DEFAULT 'ABC...';
Example 7, add multiple columns:
ALTER TABLE invoice ADD (detailname varchar2(50), numitems number(6));