INSERT INTO [users]
(business_id, id)
FROM
(
SELECT
ID - (SELECT MIN(ID) FROM [users] WHERE business_ID = B.ID) AS business_id
,(SELECT MAX(ID)+1 FROM [users] WHERE business_ID = B.ID) AS ID
FROM [businesses] B
)
se lo colleghi alle nuove voci che stai aggiungendo, dovrebbe fornire la chiave composta
Nuovo aggiornamento:
INSERT INTO [users]
(business_id, id, name)
VALUES
(
3
,ISNULL((SELECT MAX(ID)+1 FROM [users] WHERE business_ID = 3),1) AS ID
,'d'
)
