The definition of a base table can be changed by using the ALTER TABLE command, which is a schema evolution command. The possible “alter table” actions include adding or dropping a column, changing a column definition, and adding or dropping of table constraints. For example: 1. Adding a column to the Antiques table to allow the entry of the price of a given item (Parentheses optional): ALTER TABLE ANTIQUES ADD (PRICE DECIMAL(8,2) NULL); 2. Adding an attribute for keeping track of jobs of employees to the EMPLOYEE base relations in the COMPANY schema, we can use the command ALTER TABLE COMPANY.EMPLOYEE ADD JOB VARCHAR(12); 3. To drop a column we must choose either CASCADE or RESTRICT for drop behaviour. If CASCADE is chosen, all constraints and views that refernce the column are droped automatically from the schema, along with the column. If RESTRICT is chosen the command is successful only if no views are constraints reference the column. ALTER TABLE COMPANY.EMPLOYEE DROP ADDRESS CASCADE; 4. We can alter a column definition by dropping an existing default clause or by defining a new default clause: ALTER TABLE COMPANY.DEPARTMENT ALTER MGRSSN DROP DEFAULT