Query to get the number of times an item appears - php

Question

I have a table like this in my db:
id --- owner --- product ---- type
0 --- john --- mustang ---- car
1 --- tim --- a360 ---- plane
2 --- john --- camry ---- car
3 --- dan --- a380 ---- plane
4 --- tim --- ninja ---- bike
5 --- dan --- accord ---- car
I'm trying to get the number of each type an owner has. Something like this:
John
Car = 2
Plane = 0
Bike = 0
-------------
Tim
Car = 0
Plane = 1
Bike = 1
-------------
Dan
Car = 1
Plane = 1
Bike = 0
-------------
I have been unable to solve this.
Another issue is that my database is able to accept new types. For example, someone can add a bicycle as a type.
Is there any way to do this?

Answer 1

The way I approached this was a little tricky.
I started by creating one result set that used a cartesian product to get one row for each person and type combination.
SELECT m.owner, t.type
FROM myTypes t, myTable m
GROUP BY m.owner, t.type
Then, I made another result set that grabbed the owner, type, and the number of each type for that owner. However, this only returned rows for existing owner-type combinations. It would not return any values for say 'John' and 'Plane' because he does not have a plane product.
SELECT m.owner, t.type, COUNT(*) as numOfType
FROM myTypes t
JOIN myTable m ON t.type = m.type
GROUP BY t.type, m.owner;
Finally, I joined those two tables together using an outer join so I received every row from the owner-type combinations table. Of course, some rows returned null for the count, so I had to use IFNULL to replace them with 0. This matches the result set in your question.
SELECT w1.owner, w1.type, IFNULL(w2.numOfType, 0) AS numOfType
FROM (SELECT m.owner, t.type
FROM myTypes t, myTable m
GROUP BY m.owner, t.type) w1
LEFT JOIN (SELECT m.owner, t.type, COUNT(*) as numOfType
FROM myTypes t
JOIN myTable m ON t.type = m.type
GROUP BY t.type, m.owner) w2
ON w1.owner = w2.owner AND w1.type = w2.type;
Here is the SQL Fiddle.

Answer 2

To solve this problem, first you have to generate the output rows and then get the counts:
select o.owner, p.product, count(t.owner)
from (select distinct owner from table) o cross join
(select distinct product from table) p left join
table t
on t.owner = o.owner and t.product = p.product
group by o.owner, p.product;
If you have reference tables for owners and products, then you can use these instead of the select distinct subqueries.
EDIT:
Grouping by type is basically the same idea:
select o.owner, ty.type, count(t.owner)
from (select distinct owner from table) o cross join
(select distinct type from table) ty left join
table t
on t.owner = o.owner and t.type = ty.type
group by o.owner, ty.type;