Using GROUP_CONCAT on subquery in MySQL

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我在风中等你 2021-02-02 06:28

I have a MySQL query in which I want to include a list of ID\'s from another table. On the website, people are able to add certain items, and people can then add those items to

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一生所求 (楼主)

2021-02-02 06:31
Yes, soulmerge's solution is ok. But I needed a query where I had to collect data from more child tables, for example:
- main table: sessions (presentation sessions) (uid, name, ..)
- 1st child table: events with key session_id (uid, session_uid, date, time_start, time_end)
- 2nd child table: accessories_needed (laptop, projector, microphones, etc.) with key session_id (uid, session_uid, accessory_name)
- 3rd child table: session_presenters (presenter persons) with key session_id (uid, session_uid, presenter_name, address...)
Every Session has more rows in child tables tables (more time schedules, more accessories)

And I needed to collect in one collection for every session to display in ore row (some of them):
```
session_id | session_name | date | time_start | time_end | accessories | presenters
```
My solution (after many hours of experiments):
```
SELECT sessions.uid, sessions.name,
    ,(SELECT GROUP_CONCAT( `events`.date SEPARATOR '
```
') FROM `events` WHERE `events`.session_id = sessions.uid ORDER BY `events`.date) AS date ,(SELECT GROUP_CONCAT( `events`.time_start SEPARATOR '
') FROM `events` WHERE `events`.session_id = sessions.uid ORDER BY `events`.date) AS time_start ,(SELECT GROUP_CONCAT( `events`.time_end SEPARATOR '
') FROM `events` WHERE `events`.session_id = sessions.uid ORDER BY `events`.date) AS time_end ,(SELECT GROUP_CONCAT( accessories.name SEPARATOR '
') FROM accessories WHERE accessories.session_id = sessions.uid ORDER BY accessories.name) AS accessories ,(SELECT GROUP_CONCAT( presenters.name SEPARATOR '
') FROM presenters WHERE presenters.session_id = sessions.uid ORDER BY presenters.name) AS presenters FROM sessions
So no JOIN or GROUP BY needed. Another useful thing to display data friendly (when "echoing" them):
- you can wrap the events.date, time_start, time_end, etc in "
  - ...
  " so the "
I hope this helps someone. Cheers!

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