從不同的表和組減去兩列

Question

一週後搜索我不能寫這個查詢請幫助我。 我有3個表購買,selles,東西。 我想第一總和purchase.quantityselles.quantity字段分開，然後減去這兩個柱purchase.quantity selles.quantity然後GROUP BY purchase.scale，stuff.name

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我有這3臺

table purchase: 
    'id', 'invoice_id', 'stuff_id', 'quantity', 'scale', 'price' 
table selles: 
    'id', 'selles_invoice_num', 'stuff_id', 'quantity', 'scale', 'price' 
table stuff: 
    'id', 'name' 

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我有這樣的查詢，但結果（數量）是錯誤的

SELECT sum(purchase.quantity) - sum(selles.quantity) as quantities, 
     purchase.scale, 
     stuff.name , 
     stuff.id 
FROM purchase, 
    selles, 
    stuff 
where purchase.stuff_id = selles.stuff_id 
and purchase.scale = selles.scale 
and purchase.stuff_id = stuff.id 
group by purchase.scale, 
     stuff.name 
ORDER BY stuff.name , 
     purchase.scale 

Answer 1

嘗試用內部聯接

 SELECT sum(pur.psum) - sum(sca.ssum) as quantities, p.scale, st.name , st.id FROM 
stuff st INNER JOIN 
    (SELECT sum(p.quantity) as psum,p.scale,p.stuff_id FROM purchase p GROUP BY p.scale,p.stuff_id) pur 
on pur.stuff_id = st.id INNER JOIN 
    (SELECT sum(s.quantity) as ssum,s.scale,s.stuff_id FROM scale s GROUP BY s.scale,s.stuff_id) sca 
on sca.scale=pur.scale and sca.stuff_id=pur.stuff_id group by pur.scale, st.name ORDER BY st.name , pur.scale;