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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
UPDATE X
500
READ X
ROLLBACK
?
Here T10 reads a value that is updated by transaction T9 that has been aborted. Therefore T10 has read a value that would never exist in the database and hence the trouble. Here the difficulty is primarily of isolation of transaction.
What Command You Use What Day of the week were you born
Define page. The database is partitioned into some number of fixed-length blocks, which are referred to as pages.
Rules Of Data Normalisation Let us now summarise Normalisation with the help of various clean rules. The following are the necessary rules for the Normalisation process: 1.
Determine object representation As a designer, we must choose properly that when to use primitive types in representing objects and when to combine groups of related objects,
Question: The following relational database schema corresponds to a part of a database used by the Registry Department of a university. DEPARTMENT (d#, d-name, head-of-dept)
Define the Division Operation of Relational Algebra Let R be a relation comprising attributes (A1,...Ap,Ap+1,...An) and S comprising attributes (Ap+1,...An) DEF: Division
To delete a particular column in a relation which command is used ? To delete a particular column in a relation ALTER command is used.
Replication : It is definite as a copy of a relation. Every replica is stored at a dissimilar site. The alternative to replication is to store only single copy of a relation which
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Key to represent relationship amongs tables is called ? A Key that represent the relationship between tables is called Foreign Key.
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