Group by with count - sql

Question

Say I have a table like this in my MsSql server 2005 server
Apples
+ Id
+ Brand
+ HasWorms
Now I want an overview of the number of apples that have worms in them per brand.
Actually even better would be a list of all the apple brands with a flag if they are unspoiled or not.
So if I had the data
ID| Brand | HasWorms
---------------------------
1 | Granny Smith | 1
2 | Granny Smith | 0
3 | Granny Smith | 1
4 | Jonagold | 0
5 | Jonagold | 0
6 | Gala | 1
7 | Gala | 1
I want to end up with
Brand | IsUnspoiled
--------------------------
Granny Smith | 0
Jonagold | 1
Gala | 0
I figure I should first
select brand, numberOfSpoiles =
case
when count([someMagic]) > 0 then 1
else 0
end
from apples
group by brand
I can't use a having clause, because then brands without valid entries would dissapear from my list (I wouldn't see the entry Gala).
Then I thought a subquery of some kind should do it, but then I can't link the apple id of the outer (grouped) query to the inner (count) query...
Any ideas?

Answer 1

select brand, case when sum(hasworms)>0 then 0 else 1 end IsUnSpoiled
from apples
group by brand

Answer 2

SQL server version, I did spoiled instead of unspoiled, this way I could use the SIGN function and make the code shorter
table + data (DML + DDL)
create table Apples(id int,brand varchar(20),HasWorms bit)
insert Apples values(1,'Granny Smith',1)
insert Apples values(2,'Granny Smith',0)
insert Apples values(3,'Granny Smith',1)
insert Apples values(4,'Jonagold',0)
insert Apples values(5,'Jonagold',0)
insert Apples values(6,'Gala',1)
insert Apples values(7,'Gala',1)
Query
select brand, IsSpoiled = sign(sum(convert(int,hasworms)))
from apples
group by brand
Output
brand IsSpoiled
----------------------
Gala 1
Granny Smith 1
Jonagold 0

Answer 3

SELECT Brand,
1-MAX(HasWorms) AS IsUnspoiled
FROM apples
GROUP BY Brand

Answer 4

SELECT brand,
COALESCE(
(
SELECT TOP 1 0
FROM apples ai
WHERE ai.brand = ao.brand
AND hasWorms = 1
), 1) AS isUnspoiled
FROM (
SELECT DISTINCT brand
FROM apples
) ao
If you have an index on (brand, hasWorms), this query will be super fast, since it does not count aggregates, but instead searches for a first spoiled apple within each brand ans stops.

Answer 5

I haven't tested this, and maybe I'm missing something. But wouldn't this work?
SELECT Brand, SUM(CONVERT(int, HasWorms)) AS SpoiledCount
FROM Apples
GROUP BY Brand
ORDER BY SpoiledCount DESC
I assume HasWorms is a bit field, hence the CONVERT statement. This should return a list of brands with the count of spoiled apples per brand. You should see the worst (most spoiled) at the top and the best at the bottom.

Answer 6

There are many ways to skin this cat. Depending on your RDBMS, different queries will give you the best results. On our Oracle box, this query performs faster than all the others listed, assuming that you have an index on Brand in the Apples table (an index on Brand, HasWorms is even faster, but that may not be likely; depending on your data distribution, an index on just HasWorms may be the fastest of all). It also assumes you have a table "BrandTable", which just has the brands:
SELECT Brand
, 1 IsSpoiled
FROM BrandTable b
WHERE EXISTS
( SELECT 1
FROM Apples a
WHERE a.brand = b.brand
AND a.HasWorms = 1
)
UNION
SELECT Brand
, 0
FROM BrandTable b
WHERE NOT EXISTS
( SELECT 1
FROM Apples a
WHERE a.brand = b.brand
AND a.HasWorms = 1
)
ORDER BY 1;

Answer 7

SELECT CASE WHEN SUM(HasWorms) > 0 THEN 0 ELSE 1 END AS IsUnspoiled, Brand
FROM apples
GROUP BY Brand