The ALTER statement is a way to change a table's definition - i.e. to add or delete an attribute or a constraint.
Syntax of the ALTER statement
ALTER TABLE table_name ADD|DROP definition[ CASCADE]
Comments
| table_name | A name of a table to be changed |
| ADD | An attribute or a constraint has to be added |
| DROP | An attribute or a constraint has to be dropped. Not every DBMS support this. |
| definition | If ADD is specified then it is a definition of an attribute or a constraint - see the chapter CREATE for more details. Else it is the name of an attribute or a constraint to be dropped. |
| CASCADE | Because DROP can violate the reference integrity, there can be used CASCADE method to keep this integrity. Otherwise the default method is used. |