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Recovery Techniques:After Reading the types of failures and database errors, let us talk about how to recover from the failures. Recovery can be complete using/restoring the previous consistent state (backward recovery) or by moving forward to the next consistent state as per the committed transactions recovery (forward recovery). Please note that a system can recover from software and hardware failures by using the forward and backward recovery only if the system log is intact. What is the system log? We will talk about it in more detail, but first let us describe forward and backward recovery.
Why 'AS' clause is used in SQL ? 'As' clause is used for Rename operation. ‘AS' clause is used in SQL for rename operation. (e.g., SELECT ENO AS EMPLOYEE_NO FROM EMP)
In tuple relational calculus P1 → P2 is equivalent to ? A In tuple relational calculus P1→ P2 is equivalent to ¬P1 V P2. (The logical implication expression A B, meaning
Speedup Query Processing: A query that includes data at various sites can be split into sub-queries. These sub- queries can be implemented in parallel by various sites. Such parall
Differentiate between a unique key and a primary key. - By default, clustered index on column are created by primary key while nonclustered index are created by unique key.
Briefly describe concurrency execution? Lock - based protocols Locks There are several modes in which a data item may be locked in this section we restrict our attention
what are the reasons having variable length records
What is Outer join? They can be employed while we want to keep all the tuples in R, or all those in S or all those in both relations in the result of the JOIN in spite of of w
What are the states of transaction? The states of transaction are:- a) Active b) Partially committed c) Failed d) Aborted e )Committed f) Terminated
Benefits of Hashed file Organisation 1. Insertion or search on hash-key is quick. 2. Best if equality search is required on hash-key. Drawbacks of Hashed file
Benefits: It limits data access. It makes difficult queries look easy. It permits data independence. It presents dissimilar views of the similar data.
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