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Before defines the second type of integrity constraint, viz., Entity Integrity, we should be well-known with the concept of NULL.
Mostly, NULL is intended as a basis for dealing with the trouble of missing information. This type of situation is frequently encountered in the actual world. For instance, historical records sometimes have entries such as "Date of birth unknown", or police records may contain the entry "Present whereabouts unknown." Therefore it is necessary to have some way of dealing with such concepts in database systems.
Therefore Codd proposed an approach to this issue that creates use of special markers known as NULL to show such missing information.
A given attribute in the relation may or may not be allowed to include NULL. However, can the Primary key or any of its components (in case of the primary key is a composite key) contain a NULL? To answer this Query an Entity Integrity Rule states: No component of the primary key of a relation is permitted to accept NULL. In different words, the definition of each attribute involved in the primary key of any basic relation have to explicitly or implicitly contain the specifications of NULL NOT ALLOWED.
What is transaction? Transaction is a unit of program implementation that accesses and possibly updated several data items.
Wait-die" scheme : The idea is based on non-preventive method. It is based on a simple rule: If Ti requests a database resource that is held by T
Explain Superkey Ans: A superkey is described in the relational model of database organization like a set of attributes of a relation variable for which it holds that in all re
Develop C# schoolproject ASAP Helping me with schoolproject. The project is prepared in C# and haves a database connection. We have some small issues asking up data from t
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Explain Authorization and Integrity Manager ? Authorization and Integrity Manager: Tests for the satisfaction of integrity constraints and checks the authority of users to acce
Consider the 1ollowin8 relation: CAR SALE (Car_id, Option_type, Option_listprice, Sale_date, Option_discountedprice) This relation refers to options installed in cars (e.g., crui
What is 2NF? A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
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