Writable external tables allow only INSERT
operations. You must grant INSERT
permission on a table to enable access to users who are not the table owner or a superuser. For example:
GRANT INSERT ON writable_ext_table TO admin;
To unload data using a writable external table, select the data from the source table(s) and insert it into the writable external table. The resulting rows are output to the writable external table. For example:
INSERT INTO writable_ext_table SELECT * FROM regular_table;
Parent topic: Unloading Data from Greenplum Database