SQL>
SQL> CREATE TABLE myTable (
2 Name VARCHAR(50) PRIMARY KEY NOT NULL,
3 PhoneNo VARCHAR(15) DEFAULT 'Unknown Phone',
4 SSN VARCHAR(15) NOT NULL,
5 CHECK (SSN LIKE '[0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]'));
Table created.
SQL>
SQL>
SQL>
SQL> ALTER TABLE myTable DROP COLUMN PhoneNo;
Table altered.
SQL>
SQL> drop table myTable;
Table dropped.
SQL>