Performance : SQL Queries vs Server-Side PHP Loops (MYSQL vs PHP)

I have not seen much info on this topic and require some data . I am new to using complex MySQL queries and i was wondering about the performance costs of Complex queries in comparison to a simple query and then run server side php calculations on it .

E.g :

'Simple' query :

SELECT id as ID, date(x_date),  v_price as price
                From tableX
                WHERE v_price IN 
                (
                    select MIN(v_price) from tableX
                    GROUP BY week(x_date)
                )
            )

Now lets say i want to count the number of times similar prices occurred .

I can do it in 2 ways .

A) Use a foreach loop server side php and calculate the data

B) Do another select in sql

group by price
ORDER BY COUNT(price) DESC

Which is the best way to proceed ? via SQL or server code (php)

What are the performance costs , time , server load etc.....