Question

My table looks like

person_id  | car_id | miles
------------------------------
    1      |   1    |  100
    1      |   2    |  200
    2      |   3    | 1000 
    2      |   4    |  500

I need to total the miles for each person and then average those totals.

There are 2 people – person 1 drove 300 miles, person 2 drove 1500 miles.

(300+1500)/2 = 900 average number of miles driven per person.

Which is the same thing as totaling the number of miles and dividing by the number of people.

I cannot figure out a mySQL statement that will either give me the average across people or give me total the number of miles and the number of people so I can do the division.

Answer 1

Total per person:

SELECT person_id, SUM(miles) FROM table GROUP BY person_id

Average

SELECT SUM(miles) / COUNT(DISTINCT person_id) FROM table

These should work