Question

Write a SQL statement to retrieve the average number of pages per category

Answer 1

Let suppose SQLTable is the table name, It is having two columns and multiple rows

Columns are pages and category,

category is same for some of the pages and we have to find the average of pages category wise

So, here we will use , GROUP BY clause to make group of each category

After that , we will use aggregate function AVG to find the average of pages for each category

Below is the final query:

SELECT AVG(pages),category from SQLTable GROUP BY category;

Example:

Below is the table:

pages	category
90	C001
60	C001
80	C002
20	C002
20	C002

As per above query , below will be the output:

AVG(pages)	category
75	C001
40	C002

so, by GROUP BY , category goes grouped C001 and C002

and average is found groupwise,

C001 - have 60,90 - whose average is 75

C002 - have 60,20,20 - whose average is 40