mysql - MySQL，同一张表上的字段相关的元组，GROUP BY还是SELF JOIN？

Question

我有这些表（简化）：

Appointment(
    INT idAppointment,
    DATETIME start,
    DATETIME end)

AppointmentInvolved(
    INT idAppointment,
    INT idInvolved)

Involved(
    INT idInvolved,
    VARCHAR name,
    INT type,
    INT idIncident)

Incident(
    INT idIncident,
    VARCHAR description)

发生了一起事件，可能涉及到几个事件。每个 Involved 可以有多个约会，并且每个约会可以由多个 Involved 参加。涉及的有类型（本例中，principal=1，secondary=2）。

给定一个 idAppointment，我需要知道参与该事件的负责人，无论他是否要参加该特定约会。

至今：

SELECT(*)
FROM Appointments a
INNER JOIN (AppointmentInvolved ai) ON ai.idAppointment = a.idAppointment,
INNER JOIN (Involved i) ON i.idInvolved = ai.idInvolved,
INNER JOIN (Incident in) ON i.idIncident = in.idIncident,
WHERE a.idAppointment = <WHATEV>
WHERE in.type=1

除非所涉及的校长要去参加那个约会，否则这显然是行不通的。这是某种自我加入吗？我真的不需要 Incident 表，因为参与人员可以通过 idInvolved 直接关联。

谢谢！

Answer 1

SELECT * 
FROM Involved I
WHERE I.type=1 
  AND I.idIncident IN (SELECT I2.idIncident 
                       FROM AppointmentInvolved AI
                          INNER JOIN Involved I2 ON AI.idInvolved = I2.idInvolved
                          WHERE AI.idAppointment=<WHATEV>)