SQL - Group By Distinct Values - sql

Question

My question, is there a faster way to the following query?
I'm using ORACLE 10g
Say i have a table Manufacturer and Car, and i want to count all occurrences of the column 'Car.Name'. here is How i'd do it:
SELECT manuf.Name, COUNT(car1.Name), COUNT(car2.Name), COUNT(car3.Name)
FROM Manufacturer manuf
LEFT JOIN (SELECT * FROM Car c where c.Name = 'Ferrari1') car1 ON manuf.PK = car1.ManufPK
LEFT JOIN (SELECT * FROM Car c where c.Name = 'Ferrari2') car2 ON manuf.PK = car2.ManufPK
LEFT JOIN (SELECT * FROM Car c where c.Name = 'Ferrari3') car3 ON manuf.PK = car3.ManufPK
GROUP BY manuf.Name
Wanted Results:
Manufacturer | Ferrari1 | Ferrari2 | Ferrari3
----------------------------------------------
Fiat | 1 | 0 | 5
Ford | 2 | 3 | 0
I tried this with few LEFT JOINs, and it worked fine. But when i added a lot (like 90+), it was ultra slow (more than 1 minute).
My question, is there a faster way to do this query?

Answer 1

If you are happy to see the cars counted down the page, try:
select m.Name manufacturer_name,
c.Name car_name,
count(*)
from Manufacturer m
left join Car c
on m.PK = c.ManufPK and c.Name in ('Ferrari1','Ferrari2','Ferrari3')
group by m.Name, c.Name
If you need to see individual cars across the page, try:
select m.Name manufacturer_name,
sum(case c.Name when 'Ferrari1' then 1 else 0 end) Ferrari1_Count,
sum(case c.Name when 'Ferrari2' then 1 else 0 end) Ferrari2_Count,
sum(case c.Name when 'Ferrari3' then 1 else 0 end) Ferrari3_Count
from Manufacturer m
left join Car c
on m.PK = c.ManufPK and c.Name in ('Ferrari1','Ferrari2','Ferrari3')
group by m.Name

Answer 2

SELECT manuf.Name, COUNT(DISTINCT c.Name)
FROM Manufacturer manuf
LEFT JOIN Car c ON manuf.PK = c.ManufPK
GROUP BY manuf.Name
OR depending on your needs
SELECT manuf.Name, c.Name, COUNT(*) Cnt
FROM Manufacturer manuf
LEFT JOIN Car c ON manuf.PK = c.ManufPK
GROUP BY manuf.Name, c.Name
PS: Your question is not very clear. Provide some wanted resultset to refine the answer

Answer 3

You can also try this:
SELECT manuf.Name
, car1.cnt AS Ferrari1
, car2.cnt AS Ferrari2
, car3.cnt AS Ferrari3
FROM
Manufacturer AS manuf
LEFT JOIN
( SELECT ManufPK, COUNT(*) AS cnt
FROM Car
WHERE Name = 'Ferrari1'
GROUP BY ManufPK
) AS car1
ON car1.ManufPK = manuf.PK
LEFT JOIN
( SELECT ManufPK, COUNT(*) AS cnt
FROM Car
WHERE Name = 'Ferrari2'
GROUP BY ManufPK
) AS car2
ON car2.ManufPK = manuf.PK
LEFT JOIN
( SELECT ManufPK, COUNT(*) AS cnt
FROM Car
WHERE Name = 'Ferrari3'
GROUP BY ManufPK
) AS car3
ON car3.ManufPK = manuf.PK
ORDER BY manuf.Name