For this,

SELECT retailer_name, blood_type, blood_price,

COUNT(*) OVER (PARTITION BY retailer_name)

AS inventory_cnt

FROM Vampire_Retailers AS VR

WHERE blood_type = 'B';

Wouldn't you instead get nameA, 'B', 2.75, 1 and not nameA, 'B', 2.75, 2 due to the where clause?