We can read data from Oracle or MSSQL with the help of PostgreSQL Foreign Data Wrapper. Please read the following articles for installation and detailed information.
“Foreign Data Wrapper Between PostgreSQL and Oracle“,
“Foreign Data Wrapper Between PostgreSQL and MSSQL”
You have created oracle_fdw(Oracle Foreign Data Wrapper Extension) or tds_fdw(MSSQL Foreign Data Wrapper Extension) in the PostgreSQL Cluster. In order to enable the application developer to perform his / her own operations on Oracle_fdw or tds_fdw, you can authorize the user as follows.
GRANT ALL ON FOREIGN DATA WRAPPER oracle_fdw FROM pg_User
GRANT ALL ON FOREIGN DATA WRAPPER tds_fdw FROM pg_User;