Data base Management Systemdatabase

Explain any three aggregate functions with examples

Explain any three aggregate functions with examples. Aggregate Functions are keywords in SQL used to manipulate values within columns for output purposes. A function is a command always used in conjunction with a column name or expression. There are several types of functions in SQL.  An aggregate function is used to provide summarization information for an SQL statement, such as counts, totals, and averages.MIN      - returns the smallest value in a given columnMAX     - returns the largest value in a given columnSUM    - returns the sum of the numeric values in a given columnAVG     - returns the average value of a given columnCOUNT- returns the total number of values in a given columnCOUNT(*) - returns

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Data base Management Systemdatabase

Explain Database architecture

Explain Database architectureThere are following three levels or layers of DBMS architecture:• External Level•Conceptual Level• Internal LevelObjective of the Three Level ArchitectureThe objective of the three level architecture is to separate each user's view of the database from the Way the database is physically represented. There are several reasons why this separation is desirable:• Each user should be able to access the same data, but have a different customized view of the data. Each user should be able to change the way he or she views the data, and this change should not affect other users.• Users should not have to deal directly with physical database storage details, such as indexing or hashing. In other words a user's interaction with the database should be independent of stora

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Data base Management Systemdatabase

Explain the three levels in data abstraction

Explain the three levels in data abstraction.Explain the three levels in data abstraction. Three levels of data abstraction are:1. Physical level : How the data is stored physically and where it is stored in database.2. Logical level: What information or data is stored in the database (like what is the data type or what is format of data.3. View level: End users work on view level. If any amendment is made it can be saved by other name.For the database to be usable it must retrieve data efficiently. This efficiency led designer to use complex data structure in the database.

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