SQL Guide : Using SQL for database administration : Managing tables : Adding columns to a table
  
Adding columns to a table
ALTER TABLE table_name ADD COLUMN column_name column_type;
Only the creator of the particular table or users having SYS_ADMIN_ROLE have privileges to add or delete columns in a table.
The following example adds the column C of the column type CHAR(1) to the table TEST.
ALTER TABLE TEST ADD COLUMN C CHAR(1);
See also
Managing tables