Everyone has his/her own driving license, and I need to know what kind of
person (client or user) is.
mysql> select userID, clientID from client, user where
(clientCodeDrivingLicense= 321321321 || userCodeDrivingLicense = 321321321);
+--------+-------+
| userID | clientID |
+--------+-------+
| 1 | 2 |
| 2 | 2 |
| 3 | 2 |
| 4 | 2 |
| 5 | 2 |
+--------+-------+
5 rows in set (0.00 sec)
But, what I want is something like that:
+--------+-------+
| userID | clientID |
+--------+-------+
| Null | 2 |
+--------+-------+
I tried something like this:
select COUNT(DISTINCT u.userID), userID, clientID from client, user where
(clientCodeDrivingLicense = 321321321 || userCodeDrivingLicense =
321321321);
+--------------------------+--------+-------+
| COUNT(DISTINCT u.userID) | userID | clientID |
+--------------------------+--------+-------+
| 5 | 1 | 2 |
+--------------------------+--------+-------+
1 row in set (0.00 sec)
But it wont be efficient enough in the future.
I suppose my solution is an Join, but they have no intersection, so, I cant
imagine how do it
Thank you!!
Regards
Rocío Gómez Escribano
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