viewnotes/550/Database Management Systems 10CS54 VTU notes

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Explain how groupBy clause works?What is the difference between WHERE and Having? Database Management Systems - 10CS54 VTU notes 8 Marks (Dec/Jan 2014 & June/July 2015)

In many cases, we want to apply the aggregate functions to subgroups of tuples in a relation Each subgroup of tuples consists of the set of tuples that have the same value for the grouping attribute(s) ?


By:anonymousguy7799

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The function is applied to each subgroup independently SQL has a GROUP BY clause for specifying the grouping attributes, which must also appear in the SELECT clause SELECT PNUMBER, PNAME, COUNT(*) FROM PROJECT, WORKS_ON WHERE PNUMBER=PNO GROUP BY PNUMBER, PNAME
In the EMPLOYEE tuples are divided into groupseach group having the same value for the Grouping attribute DNO The COUNT and AVG functions are applied to each such group of tuples separately.
The SELECTclause includes only the grouping attribute and the functions to be applied on each group of tuples. A join condition can be used in conjunction with grouping. 

Nikhil-bharadwaj

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