SELECT count(*) AS TotalSent,
DATENAME(month, p.EventDate) as [Month],
p.SubscriberKey as SubscriberKey
FROM _Sent p
INNER JOIN [Clients_DE] B ON p.SubscriberKey = B.AccountID
WHERE p.EventDate BETWEEN GETDATE()-30 AND GETDATE()
GROUP BY p.EventDate, p.SubscriberKey
HAVING COUNT(*) > 0