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What is aggregate function? Briefly describe it?
Aggregate functions are functions that take a collection of values as input and return a one value. SQL offers 5 built-in aggregate functions:
a) Average: avg
b) Minimum:min
c) Maximum: max
d) Total:sum
e) Count:count
Average: avg
Select avg (balance)
From account
Where branch-name='perryridge'
Count :count
Select branch-name,count(distinct customer-name)
From depositior,account
Where depositor.account-number=account.account-number
groupby branch-name
Database Errors: An error is said to have occurred if the implementation of a command to manipulate the database cannot be successfully finished either due to inconsistent data or
Define the five basic operators of relational algebra? Five basic operators of relational algebra are: 1. Union (∪∪∪∪) - Selects tuples which are in either P or Q or in both
What are multiple inheritances? Multiple inheritances allow a class to inherit variables and methods from many super classes.
What are the two types of serializability? The two types of serializability is a) Conflict serializability b) View serializability
Write short notes on domain relational calculus The domain relational calculus uses domain variables that take on values from an attribute domain rather than values for whole
In the architecture of a database system which external level used? In the architecture of a database system view external level used.
The Third Normal Form (3NF) Even though, transforming a relation that is not in 2NF into a number of relations that are in 2NF take out many of the anomalies, it does not neces
Timestamps For Read operations: If TS (T) If TS (T) >= W-timestamp (Q), then the transaction T is trying to read a value of data item Q which has been written and committed
What do you understand by transitive dependencies? Define with an example any two problems that can take place in the database if transitive dependencies are available in the datab
growing phase and shrinking phase are disjoint, why ?
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