我有两个Microsoft Access表，其值如下：
Devices
| N | Desc | O | P |
+------+--------+---+---+
| 3560 | ABC | 0 | 0 | <-
| 3559 | DEF | 0 | 1 |
| 3558 | GHI | 1 | 0 |
| 3557 | JKL | 1 | 0 |
| 3548 | MNO | 0 | 0 | <-
| 3549 | PQR | 0 | 0 | <-
| 3540 | STU | 0 | 0 | <-
Notifications
id | N | Email |
---+------+-------------+
1 | 3559 | a@dom.loc | <-
2 | 3548 | a@dom.loc | <-
3 | 3548 | b@dom.loc |
4 | 3547 | b@dom.loc |
5 | 3549 | b@dom.loc |
我想提取具有O = 0和P = 0的所有Devices记录，并添加一个名为Subscribed的计算字段。仅当Notifications表中存在相同的N且Email为我提供的参数时，此字段必须为True，否则为False。
例如，如果有Email = a@dom.loc参数(即为此目的在SQL中进行硬编码(，则这应该是所需的结果：
| N | Desc | O | P | Subscribed |
+------+--------+---+---+------------+
| 3560 | ABC | 0 | 0 | False |
| 3548 | MNO | 0 | 0 | True |
| 3549 | PQR | 0 | 0 | False |
| 3540 | STU | 0 | 0 | False |
考虑到这两个表将来可能会很大，我如何在Access中执行此查询？
可能我错过了子查询SQL，这很有效：
SELECT Devices.N, Devices.Desc, Devices.O, Devices.P,
(SELECT Count(*) FROM Notifications
WHERE Notifications.N = Devices.N
AND Notifications.Email = "a@dom.loc") > 0 AS Subscribed
FROM Devices
WHERE ((Devices.O=0) AND (Devices.P=0))
编辑：在@iDevlop评论之后，我能够正确地创建LEFT JOIN变体，谢谢！
SELECT Devices.N, Devices.Desc, Devices.O, Devices.P, Not IsNull(Id) AS Subscribed
FROM Devices
LEFT JOIN (SELECT Notifications.N, Notifications.Id
FROM Notifications
WHERE (Notifications.Email = "a@dom.loc")) AS qNotif
ON Devices.N = qNotif.N
WHERE ((Devices.O=0) AND (Devices.P=0));