Sql檢索另一個表中沒有關係的字段

Question

我有2個表：Customers和Orders。客戶有很多訂單，訂單屬於客戶。訂單可以批准（由approved_at字段標記）。 我想檢索所有客戶沒有任何批准的訂單。這包括沒有任何訂單的客戶和未經批准的訂單（approved_at = null）的客戶。 我可以在沒有子查詢的單個查詢中執行此操作嗎？

Answer 1

SELECT ..., COUNT(Orders.id) AS cnt 
FROM Customers 
LEFT JOIN Orders ON (Customers.id = Orders.Customer_id) AND (Orders.approved_at is null) 
HAVING cnt = 0 

Answer 2

SELECT c.* 
FROM Customers c 
LEFT JOIN Orders o ON c.ID = o.CustomerID 
WHERE o.ID IS NULL OR c.Approved_at IS NULL