By default, processor runs same SQL every 0 seconds.
Please set Scheduling > Run Schedule to a higher value and make sure that SQL is created in such a way that upon execution it picks only new/updated records else you will see "already processed" data.
Also, if NiFi is clustered then please set Scheduling > Execution to Primary node, else all nodes will run same query and you will see each record being processed "n" times where "n" = No. of nodes in Cluster.