For Incremental load we will be using QueryDatabaseTable processor which extracts data incrementally from one table. For writing sql query which extracts data from multiple tables we are using ExecuteSQL processor.
How can we extract incremental load for a join query??
If I understand what you're trying to do, in NiFi that's a Lookup pattern so you'd likely use LookupRecord with a DatabaseRecordLookupService. Each one of those would "join" the incremental load table with the rows from the table specified by the DatabaseRecordLookupService. For multiple joins you'd have a LookupRecord with corresponding DatabaseRecordLookupService for each of them.