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Unrepeatable reads: Assume T7 reads X twice during its implementation. If it did not update X itself it could be very disturbing to see a dissimilar value of X in its next read. But this could occur if, among the two read operations, another transaction modifies X.
T7
T8
Assumed value of
X=2000
READ X
2000
UPDATE X
3000
Therefore, the inconsistent values are read and results of the transaction may be in fault.
To eliminate duplicate rows (distinct operator) Example: SELECT DISTINCT DEPTNO FROM EMP;
Consider the subsequent relation schemes: Project (Project#, Project_name, chief_architect) Employee (Emp#, Empname) Assigned_To (Project#, Emp#) Give expression i
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Write short notes on relational model The relational model uses a collection of tables to show both data and the relationships between those data. The relational model is an ex
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Explain weak and strong entity sets? Weak and Strong entity sets: A physically powerful entity set has a primary key. All tuples in the group are distinguishable through that k
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What is meant by computing the closure of a set of functional dependency? The closure of F denoted by F + is the set of functional dependencies logically implied by F.
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