我怎樣才能找到客戶與數據庫中沒有訂單？

Question

想象我有兩個表：

客戶（CUST_ID） 訂單（ORDER_ID，CUST_ID）

我怎樣才能得到所有誰沒有任何訂單的客戶？

例數據庫：

customers 
cust_id 
1 
2 
3 
4 

orders 
order_id customer_id 
1  1 
2  2 
3  3 
4  3 

So what I want to retrieve is: 

cust_id 
4 

Answer 1

通常，一個相關子查詢將執行最佳

select cust_id 
from customers 
where not exists (select * from orders 
        where orders.customer_id = customers.cust_id); 

另一種選擇是左連接/ NOT NULL組合

select c.cust_id 
from customers c 
left join orders o on o.customer_id = c.cust_id 
where o.customer_id is null; 

NOT IN有時提供的解決方案，以及

select c.cust_id 
from customers c 
where c.cust_id NOT IN (select distinct customer_id from orders); 

Check here的各種選擇和相對優勢進行了深入的討論。

Answer 2

SELECT c.cust_id 
FROM customers AS c 
LEFT JOIN orders AS o 
ON c.cust_id=o.customer_id 
WHERE o.customer_id IS NULL; 

Answer 3

您可以選擇從客戶表所在的ID沒有出現在訂單表中的所有行

select * FROM customers where cust_id NOT IN 
    (select customer_id FROM orders) 

Answer 4

SELECT a.* 
FROM Customers a 
     LEFT JOIN Orders b 
      ON a.Cust_ID = b.Customer_ID 
WHERE b.Customer_ID IS NULL 

Answer 5

試試這個

select * from customers where cust_id not in (select distinct customer_id from orders) 

Answer 6

select c.cust_id 
from customers c 
left join orders o on o.customer_id = c.cust_id 
where o.customer_id is null; 

嘗試在可能的情況下避免子查詢 - 它們可能會造成可怕的性能下降。