Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Foreign Keys and NULL
Let us take the relation:
DEPT
DEPT ID
DNAME
BUDGET
D1
Marketing
10M
D2
Development
12M
D3
Research
5M
EMP
ID
ENAME
SALARY
E1
Rahul
40K
E2
Aparna
42K
E3
Ankit
30K
E4
Sangeeta
35K
Assume that Sangeeta is not assigned any section. In the EMP tuple corresponding to Sangeeta, thus, there is no genuine section number that can serve as the appropriate value for the DEPTID foreign key. Thus, one cannot verify BUDGET and DNAME for Sangeeta's department as those values are NULL. This may be actual circumstances where the person has newly joined and is undergoing training and will be allocated to a department only on finishing of the training. Thus, NULL in foreign key values might not be a logical error.
Thus, the foreign key definition may be redefined to conatin NULL as an acceptable value in the foreign key for which there is no require to find a matching tuple.
Is there any other constraint that may be applicable on the attribute values of the entities?
Yes, these constraints are mostly linked to the domain and termed as the domain constraints.
Discuss the methods for a hash file to expand and shrink dynamically. What are the advantages and disadvantages of each? The hashing methods that permit dyanamic file expansi
Explain what is Aggregation? Aggregation: Aggregation is an significant concept in database design whereas composite objects could be modelled during the design of database a
it can be possible to create any table without primary key
Define weak and strong entity sets? Weak entity set: entity set that do not have key attribute of their own are known as weak entity sets. Strong entity set: Entity set that
Explain the cartesian product in Database Management System
Types Of Indexes One of the words used during the file organisation is the term index. In this part, let us describe this term in more detail. We find the index of keywords
What is SQL Server Agent? SQL Server agent plays a significant role in the day-to-day tasks of a database administrator (DBA). It is often overlooked as one of the major tools
Determine the language that needs a user to specify the data to be retrieved with no specifying exactly how to get it is Ans: Non-Procedural DML
What is relational model feature? A relational model feature is much more data independence than some other database models.
What are stored and derived attributes? Stored attributes: The attributes keeps in a data base are known as stored attributes. Derived attributes: The attributes that are de
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!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd