MySQL group_concat met select binnen select

Ik denk dat dit is wat u zoekt, of waarmee u aan de slag kunt:

SELECT
    t.therapist_name,
    dl.day,
    GROUP_CONCAT(DISTINCT dl.name SEPARATOR ',') AS locations
FROM
    therapists t 
    LEFT JOIN days_location dl ON dl.therapist_id = t.id
    LEFT JOIN location l ON dl.location_id = l.id
GROUP BY t.therapist_name, dl.day

Voor therapists.id = 1 dit zou je resultaten moeten opleveren:

+----------------+-----------+-----------------------+
| therapist_name |    day    |       locations       |
+----------------+-----------+-----------------------+
| Therapist 1    | monday    | Location 1,Location 2 |
| Therapist 1    | wednesday | Location 3            |
| Therapist 1    | friday    | Location 1            |
+----------------+-----------+-----------------------+

Als u day moet samenvoegen met locations kolom gebruik dan een eenvoudige CONCAT() :

SELECT
    therapist_name,
    CONCAT(day, '(', locations, ')') AS locations
FROM (  
    SELECT
        t.therapist_name,
        dl.day,
        GROUP_CONCAT(DISTINCT dl.name SEPARATOR ',') AS locations
    FROM
        therapists t 
        LEFT JOIN days_location dl ON dl.therapist_id = t.id
        LEFT JOIN location l ON dl.location_id = l.id
    GROUP BY t.therapist_name, dl.day
    ) t
GROUP BY therapist_name, locations

Uitvoer zou er als volgt uit moeten zien:

+----------------+-------------------------------+
| therapist_name |           locations           |
+----------------+-------------------------------+
| Therapist 1    | monday(Location 1,Location 2) |
| Therapist 1    | wednesday(Location 3)         |
| Therapist 1    | friday(Location 1)            |
+----------------+-------------------------------+

Als u alles voor elke therapeut in één rij moet groeperen, kunt u GROUP_CONCAT() nogmaals.

Bewerken na opmerkingen :

SELECT
    therapist_name,
    GROUP_CONCAT( CONCAT(day, '(', locations, ')') SEPARATOR ',' ) AS locations
FROM (      
    SELECT
            t.therapist_name,
            dl.day,
            GROUP_CONCAT(DISTINCT dl.name SEPARATOR ',') AS locations
    FROM
            therapists t 
            LEFT JOIN days_location dl ON dl.therapist_id = t.id
            LEFT JOIN location l ON dl.location_id = l.id
    GROUP BY t.therapist_name, dl.day
    ) t
GROUP BY therapist_name

Ik heb de code niet getest, dus er kunnen enkele kleine fouten zijn om aan te passen. Geen manier om het te testen atm.