MySQL 组 Concat 在派生表上

Question

So I have a derived table and I would like to do a GROUP_CONCAT() on the derived table while still getting all the columns of the derived table

For example, I have a table called patient and one called appointment, and I would like to get a GROUP_CONCAT() of appointment IDs per patient with given criteria.

Right now I am doing something like this:

SELECT
  t1.*
FROM
  (
    SELECT
      patient.name,
      patient.ptid,
      appointment.date
    FROM
      patient
      LEFT JOIN appointment ON appointment.patient_id = patient.ptid
     /* a **lot** of filters, additional joins, etc*/
  ) t1
  LEFT JOIN (
    SELECT
      GROUP_CONCAT(appointment.appt_id) appointments,
      patient.ptid
    FROM
      patient
      LEFT JOIN appointment ON appointment.patient_id = patient.ptid
    GROUP BY
      patient.id
  ) t2 
  ON t1.ptid = t2.ptid

But the problem is that the GROUP_CONCAT() doesn't take any of the filters or anything else from the first derived table into consideration. There can also be upwards of 20 million appointment records so I feel like the additional join is just doing unnecessary work...Any advice on how to work around this? Thanks

Answer 1

I think the second subquery should be like this. Because I think we don't need to join tables there.

    SELECT
      patient_id, 
      GROUP_CONCAT(appointment.appt_id) appointments,
    FROM
      appointment
    GROUP BY
      patient_id