Database Management System Lecture - 27 © Virtual University of Pakistan

© Virtual University of Pakistan Alter Table Statement Purpose is to make changes in the definition of a table already created through Create statement Can add, drop attributes or constraints, activate or deactivate constraints; the format is © Virtual University of Pakistan

© Virtual University of Pakistan ALTER TABLE table { [ ALTER COLUMN column_name     { new_data_type [ ( precision [ , scale ] ) ]         [ NULL | NOT NULL ]     ]     | ADD         { [ < column_definition > ]         |  column_name AS computed_column_expression         } [ ,...n ]     | DROP         { [ CONSTRAINT ] constraint_name             | COLUMN column } [ ,...n ]     | { CHECK | NOCHECK } CONSTRAINT         { ALL | constraint_name [ ,...n ] } } © Virtual University of Pakistan

© Virtual University of Pakistan Alter Table Command ALTER TABLE Student add constraint fk_st_pr foreign key (prName) references Program (prName) ALTER TABLE program add constraint ck_totSem check (totSem < 9) © Virtual University of Pakistan

Removing or Changing Attribute ALTER TABLE student ALTER COLUMN stFName char(20) Alter table student drop column curSem drop constraint ck_st_pr © Virtual University of Pakistan

Removing Rows and Tables TRUNCATE TABLE table_name Truncate table class Delete can also be used DROP TABLE table_name © Virtual University of Pakistan

Data Manipulation Language Insert Select Update © Virtual University of Pakistan

© Virtual University of Pakistan Insert Statement To insert records into tables INSERT [ INTO] table       {    [ ( column_list ) ]         { VALUES             ( { DEFAULT | NULL | expression } [ ,...n] )          }     }     | DEFAULT VALUES © Virtual University of Pakistan

Database Management System Lecture - 27 © Virtual University of Pakistan