I have been using both Oracle and PostgreSQL DBMS's heavily for quite some time, and it's not clear, to me at least, what you mean when you write you want to "extract the header of a table from oracle database". For the same reason, it's not clear what "execute a create statement to store the header into postgresql" means.
Let's assume that by "the header of a table", you mean the output of Oracle's Describe command, which provides the user with a display indicating the structure of the specified table, including the column names and the data type for each column. If that assumption is correct, perhaps you mean that you'd like to use NiFi to obtain the structure of a table in Oracle, and have it CREATE a similar table in postgresql, by translating in some automated fashion between the datatypes available on that specific source Oracle database and the data types available in the target PostgreSQL database.
That is typically something that you'd do only once per schema pair. Does your task involve many database tables, and are you going to have to do this task over and over again?
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