Drop and Alter Table Constructs The drop table command deletes all information about the dropped relation from the database. The alter table command is used to add attributes to an existing relation: alter table r add A D where A is the name of the attribute to be added to relation r and D is the domain of A. All tuples in the relation are assigned null as the value for the new attribute. The alter table command can also be used to drop attributes of a relation: alter table r drop A where A is the name of an attribute of relation r Dropping of attributes not supported by many databases Database System Concepts,5th Edition,Oct 5,2006 3.8 Silberschatz,Korth and SudarshanDatabase System Concepts, 5 3.8 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Drop and Alter Table Constructs The drop table command deletes all information about the dropped relation from the database. The alter table command is used to add attributes to an existing relation: alter table r add A D where A is the name of the attribute to be added to relation r and D is the domain of A. All tuples in the relation are assigned null as the value for the new attribute. The alter table command can also be used to drop attributes of a relation: alter table r drop A where A is the name of an attribute of relation r Dropping of attributes not supported by many databases