SQL – Data Definition - 3

DROP TABLE….

• Delete table definition permanently from the database
• DROP TABLE Modules
• Can not recover again unless you use a database backup

MODIFYING TABLES…

• Add an extra column
• Drop a column
• Modify the data type or length
• Add a new table constraint
• Drop a table constraint
• Change a column property (Ex: DEFAULT VALUE, NULL NOT NULL, etc)

ALTER TABLE…

• ALTER TABLE Lecturers

          ADD COLUMN roomNo SMALLINT

• ALTER TABLE Lecturers

         ALTER COLUMN staffName VARCHAR(20)

• ALTER TABLE Lecturers

        DROP COLUMN staffName 

• ALTER TABLE Lecturers

       ALTER COLUMN level SET DEFAULT 3