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Discuss the differences among the candidate keys and the primary key of a relation. Give instance to describe your answer?
A candidate key is one that can be used as primary key which not null and unique constraint both is holding true. In short all primary keys are definitely candidate keys. That is one of the candidate keys is selected as primary key.
Shared lock or Read Lock It is requested by a transaction that needs to just read the value of data item. A shared lock on a data item does not permit an exclusive lock
Performance of Various Concurrency Control Mechanisms
Dirty Reads: T10 reads a value which is updated by T9. This update has not been committed and T9 aborts. T9 T10 Value of x old value = 200
Explain Instance and schemas? Instances and schemas: Databases changes over time as the information is deleted and inserted. The collection of information stored in database
Draw an entity relationship diagram (ERD) for the following situation: A company has a number of employees. Each employee is identified by an Employee_Id. The company wants to st
What is called a query evaluation plan? A sequence of primitive operations that can be used to assess a query is a query evaluation plan or a query implementation plan.
Modify a sequence: ALTER SEQUENCE SEQSS INCREMENT 2 MAXVALUE 3000; Removing a sequence: DROP SEQUENCE SEQSS;
What is Asterisk in SQL? Asterisk (*): In SQL, the columns for all the tables and views in the FROM clause will be displayed.
Data independence seems that "the application is independent of the access strategy and storage structure of data". In other words, the ability to change the schema definition in o
client server architeutre
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