Unusual SQL query

Question

I'm trying to find a MySQL query for the following question:

How many articles are being supplied by exactly one supllier

• The articles are in the table artikel
• The suppliers are in the table leverancier
• The table connecting them is the inkart table

The query I got so far is:

SELECT 
    COUNT(artikel.art)
FROM
    artikel
        JOIN
    inkart ON artikel.art = inkart.art
        JOIN
    leverancier ON inkart.lev = leverancier.lev
GROUP BY artikel.art
HAVING COUNT(leverancier.lev) = 1

But this is giving me the wrong (no) result. I figured I have to use a subquery somewhere, but I have no idea how.

Answer 1

select count(artikel.art)
from artikel
where 1= (select count(*) from inkart
           join leverancier on inkart.lev=leverancier.lev
           where inkart.art=artikel.art
         )

Answer 2

You only need to count unique leverancier.lev, this will give list of artikel.art

SELECT artikel.art
FROM   artikel
        JOIN inkart ON artikel.art = inkart.art
        JOIN leverancier ON inkart.lev = leverancier.lev
GROUP  BY artikel.art
HAVING COUNT(DISTINCT leverancier.lev) = 1

if you want the count of articles,

SELECT COUNT(*)
FROM
(
    SELECT artikel.art
    FROM   artikel
            JOIN inkart ON artikel.art = inkart.art
            JOIN leverancier ON inkart.lev = leverancier.lev
    GROUP  BY artikel.art
    HAVING COUNT(DISTINCT leverancier.lev) = 1
) a