加入不工作在我的SQL

Question

SELECT DISTINCT c.fname, 
s.description FROM customer c INNER JOIN orders o ON c.customer_num = 
o.customer_num INNER JOIN items i ON o.order_num = i.order_num INNER 
JOIN stock s on s.stock_num = i.stock_num WHERE i.manu_code = 'ANZ'; 

Answer 1

我很確信JOIN是在MySQL中「工作」。

（我可以在這裏補充一點，證明了它的工作原理的例子。）

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編輯

如果你有「共同的」兩個表之間的兩列，並要在連接謂詞的相等比較中引用兩個列，只需在現有的ON子句中添加AND col2 = col2 ...

例如，要添加條件cust_id等於customer和orders

SELECT DISTINCT c.fname 
     , s.description 
    FROM customer c 
    JOIN orders o 
     ON o.customer_num = c.customer_num 
    AND o.cust_id  = c.cust_id 
    -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  add this line 
    JOIN items i 
     ON i.order_num = o.order_num 
    JOIN stock s 
     ON s.stock_num = i.stock_num 
    WHERE i.manu_code = 'ANZ'; 

如果您想對要麼customer_num或cust_idcustomer和orders之間加入之間

，您可以用 OR更換 AND。 （但是這是一個奇怪的模式，有兩個不同的列匹配;這不是規範模式。）