使用sql查询中存在两种情况

Question

我正在试图做一个查询，说If the customer has no invoice, but has an appointment in the last 6 months, please give me their clientId and name以下结果返回并设置为空。

SELECT clients.clientId, clients.studentFirstName, clients.studentLastName 
FROM clients, invoices, appointments 
WHERE (NOT EXISTS 
      (SELECT * 
      FROM invoices, clients 
      WHERE invoices.clientId = clients.clientId)) 
AND (EXISTS 
     (SELECT * FROM appointments, clients 
     WHERE appointments.clientId = invoices.clientId 
     AND appointments.date >= DATE_ADD(curdate(), INTERVAL 6 MONTH))); 

编辑：该结束了查询工作是约翰的回答有点扭捏之后创建的：

SELECT a.clientID, 
    a.studentFirstName, 
    a.studentLastName 
FROM clients a 
     LEFT JOIN invoices b 
      on a.clientID = b.clientID 
     LEFT JOIN appointments c 
      on a.clientID = c.clientID 
WHERE b.clientId IS NULL AND 
    c.`date` >= DATE_SUB(curdate(), INTERVAL 6 MONTH) 

Answer 1

使用LEFT JOIN代替。

SELECT a.ClientID, 
     a.studentFirstName, 
     a.clients.studentLastName 
FROM clients a 
      LEFT JOIN invoices b 
       on a.ClientID = b.ClientID 
      LEFT JOIN appointments c 
       on a.ClientID = c.ClientID 
WHERE b.Client IS NULL AND 
     c.`Date` >= DATE_SUB(curdate(), INTERVAL 6 MONTH) 

Answer 2

你确定它应该是DATE_ADD而不是DATE_SUB？

您可以使用联接：

SELECT a.clientId, 
      a.studentFirstName, 
      a.studentLastName 
FROM  clients a 
JOIN  appointments b ON a.clientId = b.clientId 
      AND b.date >= CURDATE() - INTERVAL 6 MONTH 
LEFT JOIN invoices c ON a.clientId = c.clientId 
WHERE  c.clientId IS NULL