Question

我想获取尚未包含在Customer_Machine表中的序列号。但相反，行是交叉乘法。这是我的代码。

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 )

有什么帮助吗？

Answer 1

这应该做：

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)

您现在正在做的是加入customer_machine来自serial_no的{{1}}来自serial_number的与customer_machine相同的数字;所以你的结果会倍增。

Answer 2

如果您加入Product和serial_number表，结果将为serial numbers which are in products but not in customer_machine。由于上述答案处理了这种情况，因此该查询将使用serial numbers which are not in customer_machine并忽略left join表来选择Product（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 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

您可能只想排除已存在的特定序列号，而不是将它们加入。您可以在where子句中执行此操作：

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 )

交叉乘法查询

4 个答案: