交叉倍增查詢

Question

我喜歡獲取尚未包含在Customer_Machine表中的序列號。但相反，這些行是交叉相乘。這是我的代碼。

SELECT serial_number.serial_no 
FROM product 
     INNER JOIN serial_number 
       ON product.productid = serial_number.productid 
     INNER JOIN customer_machine 
       ON NOT(customer_machine.serial_no = serial_number.serial_no) 

任何幫助嗎？

Answer 1

如果你加入Product和serial_number表，結果將是serial numbers which are in products but not in customer_machine。由於上述答案處理該情況，因此此查詢將使用left join並忽略Product表來選擇serial numbers which are not in customer_machine（如您所述）。

Sql-Server fiddle demo

select s.serial_no 
from serial_number s 
    left join customer_machine c on s.serial_no = c.serial_no 
where c.serial_no is null 

Answer 2

這應該這樣做：

SELECT serial_number.serial_no 
FROM product P 
INNER JOIN serial_number S 
     ON P.productid = S.productid 
WHERE NOT EXISTS (SELECT 1 FROM customer_machine 
        WHERE serial_no = S.serial_no) 

你現在正在做的，與customer_machine從serial_number不與customer_machine相同數量的匹配連接，每serial_no;所以你正在增加你的結果。

Answer 3

SELECT serial_number.serial_no 
FROM product 
     INNER JOIN serial_number 
       ON product.productid = serial_number.productid 
     LEFT JOIN customer_machine 
       ON (customer_machine.serial_no = serial_number.serial_no) 
WHERE customer_machine.serial_no IS NULL 

Answer 4

你可能只是想排除已存在的特定序列號，而不是將它們連接您可以在WHERE子句中做到這一點：

SELECT serial_number.serial_no 
FROM product 
INNER JOIN serial_number 
      ON product.productid = serial_number.productid 
WHERE serial_number.serial_no NOT IN (SELECT customer_machine.serial_no 
             FROM customer_machine)