MySQL joins og COUNT(*) fra en anden tabel

MySQL-brug HAR redegørelse for disse opgaver.

Din forespørgsel ville se sådan ud:

SELECT g.group_id, COUNT(m.member_id) AS members
FROM groups AS g
LEFT JOIN group_members AS m USING(group_id)
GROUP BY g.group_id
HAVING members > 4

eksempel når referencer har forskellige navne

SELECT g.id, COUNT(m.member_id) AS members
FROM groups AS g
LEFT JOIN group_members AS m ON g.id = m.group_id
GROUP BY g.id
HAVING members > 4

Sørg også for, at du indstiller indekser i dit databaseskema for nøgler, du bruger i JOINS, da det kan påvirke dit websteds ydeevne.