Alter table command, Database Management System

Assignment Help:

ALTER TABLE Command: This command is used for variation of existing structure of the table in the given situation:

  • When a new column is to be added to the table structure.
  • When the existing column definition has to be altered, i.e., changing the width of the data type or the data type itself.
  • When integrity constraints have to be dropped or included.
  • When a constraint has to be allowed or not allowed.

Syntax

ALTER TABLE

ADD ( ...); ALTER TABLE
MODIFY ( ...);

ALTER TABLE

ADD CONSTRAINT < constraint type>(field name);

ALTER TABLE

DROP;

ALTER TABLE

ENABLE/DISABLE ;

You require to put many constraints like that the database integrity is not compromised.

 


Related Discussions:- Alter table command

What is authorization graph, What is authorization graph? Passing of au...

What is authorization graph? Passing of authorization from single user to another can be shown by an authorization graph.

What are the advantages of having an index structure, What are the advantag...

What are the advantages of having an index structure?      Ans: The index structures commonly provide secondary access paths, which offer alternative ways of accessing the reco

Creating views with replace option, Creating views with Replace option : Th...

Creating views with Replace option : This option is used to alter the definition of the view without recreating and dropping it or regranting object privileges previously granted o

List the armstrong axioms for functional dependencies, List the Armstrong's...

List the Armstrong's axioms for functional dependencies.  What do you understand by soundness and completeness of these axioms?      Ans: The Armstrong's axioms are: F1:

Create a view containing name and number of department, Create a view emp_d...

Create a view emp_dep containing e_name and number of dependents from the tables employee and dependent of (i) CREATE VIEW emp_dept AS SELECT ename, COUNT(*) FROM employee, dep

Modelling and normalisation, Task Part A. Create an ERD from a business pro...

Task Part A. Create an ERD from a business problem. (50 marks) Read the following problem and complete the tasks listed below. THE ABS Blood Bank Australian Blood Services (ABS) i

Define multivalued dependency and 4nf, Define multivalued dependency and 4N...

Define multivalued dependency and 4NF.  Ans:  Multivalued Dependency - Assume R be a relation schema and let α ⊆ R and β ⊆ R. The multivalued dependency  α →→β   holds o

State the object design for processing, State the Object Design for Process...

State the Object Design for Processing  The object design phase comes after analysis and system design phase. The object design phase includes implementation details like as i

Need for a database management system, NEED FOR A DATABASE MANAGEMENT SYSTE...

NEED FOR A DATABASE MANAGEMENT SYSTEM A Database is a structured, persistent collection of data of an organisation. The database management system (DBMS) manages the database o

What is a relationship called when it is maintained entities, What is a rel...

What is a relationship called when it is maintained between two entities? A relationship is called Binary relationship when it is maintained between two entities.

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd