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Define Aggregate functions and what aggregate functions supported by the MySQL
To calculate a summary value from a set of individual values and uses one of the functions known as aggregate functions.
These are so called for the reason that they operate on aggregates (groups) of values.
Aggregate functions include COUNT ( ) which counts records or values in a query result; MAX( ) and MIN( ) which find largest and smallest values; SUM( ) and AVG( )and which produce sums and means of values.
The Database administrator (DBA) uses the data dictionary in each phase of a database life cycle, beginning from the data gathering phase to the design, execution and maintenance p
What is a transaction ? The Transaction is a unit of data processing. For instance, many of the transactions at a bank may be withdrawal or deposit of money; transfer of money f
Example: //REVOKE ALL ON EMP FROM MCA12; (All permissions will be cancelled) You can also cancel only some of the permissions. Drop: A user-
What is a PROJECT operation? The project operation is a unary operation that returns its argument relation with particular attributes left out. Projection is shown by pie (π).
It defines that the tuple in one relation that refers to another relation must refer to an existing tuple in that relation. This constraint is states on two relations (not essentia
Data Redundancy -A lot of information is being repeated in the relation. For instance, the information that MCS-014 is named SSAD is repetitive, address of Rahul is "D- 27, Main ro
Describe briefly models which define the operations on classes. The three models which are used to define operations on classes are as: Object Model = data dictionary + Obje
assignment
What are the three classes of SQL expression? SQL expression consists of three clauses: Select From Where
Given the following relations Vehicle (Reg_no, make, colour) Person(eno, name, address) Owner(eno, reg_no) Write expressions in the relational algebra to answer the following
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