1. Database Management System
Lecture - 27
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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
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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 ] } }
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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)
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5. Removing or Changing Attribute
ALTER TABLE student
ALTER COLUMN stFName char(20)
Alter table student
drop column curSem
drop constraint ck_st_pr
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6. Removing Rows and Tables
TRUNCATE TABLE table_name
Truncate table class
Delete can also be used
DROP TABLE table_name
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7. Data Manipulation Language
Insert
Select
Update
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Insert Statement
To insert records into tables
INSERT [ INTO] table       {    [ ( column_list ) ]         { VALUES             ( { DEFAULT | NULL | expression } [ ,...n] )          }     }     | DEFAULT VALUES
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9. Database Management System
Lecture - 27
© Virtual University of Pakistan