Re: update a table in one schema from a table in another schema
As long as you have your tables in the same database (Forget about Federated DB for a while), you can perform any join between your tables. Just use the fully qualified table name. If table name is TABLENAME and schema name is SCHEMA_NAME, then the fully qualified name is SCHEMA_NAME.TABLENAME.
I am sorry, I can not get the second part of your query.
What do you want to update - a column for all rows or create records in schemaB.tableB which are not present in schemaA.tableA.