A book I've found very usefull is 'MySQL and mSQL' by O'Reilly
You could use a query like this, but...
select distinct item_number from Attributes where attribute like 'football'
and value like 'nfl'
You will be happier if you rethink your layout and create multiple tables.
Give them unique
Or:
SELECT DISTINCT T1.item_number
FROM Attributes t1, Attributes t2, Attributes t3
WHERE
t1.item_number=t2.item_number
AND t2.item_number=t3.item_number
AND t1.attribute='sport' AND t1.value='football'
AND t2.attribute='league' AND t2.value='nfl'
AND t3.attribute='typeb' AND t3.value='jersey';
