SQL query creation - mysql

Question

I have to do a query without using views that displays the automobile brand that has the maximum number of cars that have a single owner.
that's the table that I have
CAR(idcar, brand, name, year_p)
OWNER(idowner,name, b_date)
PROPERTY(idcar,idowner,date_b, date_s)
That's what I was writing..
SELECT Car.brand, COUNT(PROPERTY.idowner) as con
FROM PROPERTY JOIN CAR ON Car.idcar=Property.idcar
GROUP BY Car.brand
ORDER BY con ASC
LIMIT 1;
It's ok? what I can do to improve it?
That's how it should work
CAR
-----------------
1|FIAT|test1|2000
2|Alfa|test2|2011
3|FIAT|test3|2001
4|Alfa|test4|2006
5|Alfa|test5|2004
OWNER
-----------
1|John|1990
2|Jack|1980
3|Sam |1991
4|Rick|1980
5|Cris|1993
6|Holm|1992
PROPERTY
-------------
1|1|2000|2000
2|1|2001|2003
3|2|2000|2004
1|3|2002|2005
4|4|2004|2006
5|6|2003|2008
2|5|2001|2009
So the query should return Alfa because I've 3 people that have only one car and those 3 people have one alfa ( so 3 alfa). It can't be FIAT because I only have 2 people with only one car that is a FIAT(so 2 FIAT). The OWNER n1 is excluded because he has 2 car

Answer 1

I think you were on the right path with your query, it's only need a little modification...
First if you want to select brand with most owner than you should order them in descending order so the max will be at the top... And second you need to add WHERE clause which will exclude all owner that have more then one car...
It should look like this:
SELECT c.brand, COUNT(p.idowner) as con
FROM PROPERTY p
JOIN CAR c
ON c.idcar=p.idcar
WHERE p.idowner NOT IN (SELECT idowner
FROM (SELECT idowner, COUNT(idowner) as c
FROM PROPERTY
GROUP BY idowner) x
WHERE c > 1)
GROUP BY c.brand
ORDER BY con DESC
LIMIT 1;
Here is the SQL Fiddle to take a look how it's work...
GL!

Answer 2

This is too long for a comment.
Your query is not correct. It returns the brands that have the most properties for its cars. That may or may not have to do with the number of owners. I'm sure there's a relationship of some sort ("no properties" --> "no owners" and vice versa).
In any case, I don't know what you mean by "the maximum number of cars that have a single owner". You should edit your question with sample data and desired results. A SQL Fiddle would also be helpful.

Answer 3

--CTE to Get single owner
WITH CTEsingleowner(ct, idowner)
AS (SELECT Count(1) AS ct,
idowner
FROM property WITH(nolock)
GROUP BY idowner
HAVING Count(1) = 1)
-- Select brand with maximum number of single owner
-- with ties is used to resolve confilict more than one record set returned
SELECT TOP (1) WITH ties Count(1) AS cnt,
brand
FROM CTEsingleowner ct
JOIN property p WITH(nolock)
ON p.idowner = ct.idowner
JOIN car c WITH(nolock)
ON ( c.idcar = p.idcar )
GROUP BY brand
ORDER BY cnt DESC ;
--CTE to Get single owner
WITH CTEsingleowner(ct, idowner)
AS (SELECT Count(1) AS ct,idowner
FROM property WITH(nolock)
GROUP BY idowner
HAVING Count(1) = 1)
-- Select brand with maximum number of single owner
-- with ties is used to resolve conflict more than one rows returned
SELECT TOP (1) WITH ties Count(1) AS cnt, brand
FROM CTEsingleowner ct
JOIN property p WITH(nolock)
ON p.idowner = ct.idowner
JOIN car c WITH(nolock)
ON ( c.idcar = p.idcar )
GROUP BY brand
ORDER BY cnt DESC ;