Question

what aggregate functions priobably would be usefull to school administrators to analyze student population and why? (school environment database management)

Answer 1

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In database management an aggregate function is a function where the values of multiple rows are grouped together as input on certain criteria to form a single value of more significant meaning.

Some of the various aggregate functions are-:

1) Count()
2) Sum()
3) Avg()
4) Min()
5) Max()

These could be used in a normal school management system in counting like total students in a school or in a particular stream or class, calculating average number of boys in each class, class with minimum number of boys/girls or the maximum number of boys/girls etc.

Suppose we have given data-:

Total     Section     Number of boys      Number of girls
---------------------------------------------------------
120       A            80                      60
90        B            40                      50
105       C            60                      45
105       D            70                      35
85        E            60                      25  
95        F            50                      45  

// The normal way to write a query is like this:

SELECT COUNT(*) AS NumStudents FROM table_name;

i) If we want to calculate the number of sections with equal/distinct number of students then count() can be used--

Count(Distinct Total): Return number of distinct Non Null values over the column Total

ii) If we want to calculate the sum of Total students where total is same/distinct then sum() can be used---

sum(Total): Sum all Non Null values of Column salary

sum(Distinct Total): Sum of all distinct Non-Null values

iii) Avg(Number of girls) = Sum(number of girls) / count(number of girls)

And also

Min(Number of boys): Minimum value in the Number of boys column except NULL i.e., 40.
Max(Number of girls): Maximum value in the Number of girls column i.e., 60.

This was just a example to show how these aggregates can be used in the school management system to solve queries regarding population of students....

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