Вы можете использовать GROUP BY
и FOR JSON
:
SELECT MIN(ID) AS ID, UserId, MIN(sub.x) AS Platforms, MIN(sub2.x) AS Transactions
FROM tab t
OUTER APPLY (SELECT CONCAT('p', platformId) AS platform, cnt
FROM (SELECT PlatformId, COUNT(*) AS cnt
FROM tab t2 WHERE t2.UserId = t.UserId
GROUP BY PlatformId) s
FOR JSON AUTO) sub(x)
OUTER APPLY (SELECT CONCAT('t', TransactiontypeId) AS Transactions, cnt
FROM (SELECT TransactiontypeId, COUNT(*) AS cnt
FROM tab t2 WHERE t2.UserId = t.UserId
GROUP BY TransactiontypeId) s
FOR JSON AUTO) sub2(x)
GROUP BY UserId;
Демоверсия DBFiddle
Результат немного отличается (массив ключевого значения), но, пожалуйста, рассматривайте его как отправную точку.