SQL Guide : Using SQL for database administration : Managing tables : Deleting columns from a table
  
Deleting columns from a table
ALTER TABLE table_name DROP COLUMN column_name;
A column cannot be dropped if it is part of a unique constraint or primary key. For details on primary keys, read Managing indexes.
The following example statement deletes the column C from the table TEST.
ALTER TABLE TEST DROP COLUMN C;
Note If the autocommit mode is set OFF, you need to commit your work before you can modify the data in the table you altered. To commit your work after altering a table, use the following SQL statement:
COMMIT WORK;
If the autocommit mode is set ON, then all statements, including DDL (Data Definition Language) statements, are committed automatically.
See also
Managing tables