Chcę mieć trzy tabele w kwerendzie sql, ale otrzymuję komunikat o błędzie.

Mam ten kod sql:

 SELECT warehouse.expiry_date, pharmacy.expiry_date, drugs.active_substance, 
 drugs.strength, drugs.strength_type, drugs.dosage_form, drugs.minimum_quantity, 
 SUM(warehouse.in_quant)+SUM(pharmacy.in_quant)-SUM(warehouse.out_quant)-
 SUM(pharmacy.out_quant) AS Total_available_stock

 FROM drugs as a 
  INNER JOIN warehouse as b
    ON a.ID = b.drug_id 
  INNER JOIN pharmacy as c 
    ON b.drug_id = c.drug_id
 GROUP BY warehouse.expiry_date, pharmacy.expiry_date, drugs.active_substance, 
 drugs.strength, drugs.strength_type, drugs.dosage_form, drugs.minimum_quantity;

I mam błąd:

 Syntax error (missing operator) in query expression in 'a.ID = b.drug_id 
 INNER JOIN pharmacy as c
     on b.drug_id = c.drug_i'.

Jakaś pomoc proszę?