Using Triggers with FEDERATED Tables
The question was asked if triggers could be used with FEDERATED tables, and I verified that triggers could indeed be created on FEDERATED tables. With the assertion that the a trigger on a FEDERATED table did not actually fire, I set up a base table and an associated FEDERATED tables with triggers attached to both tables and verified they did in fact get called.
A 'before insert' trigger on a FEDERATED table gets called before the corresponding 'before insert' trigger on the base table, and this is rather what I would expect. If the FEDERATED table's trigger makes an alteration to the row, the altered version is what the base table's trigger is presented with.
An 'after insert' trigger on a FEDERATED table gets called after the corresponding 'after insert' trigger on the base, and this is again what I would expect. However, there is an anomaly here. If the base table's 'before insert' trigger made alterations to the row which subsequently were written to the table, the base table's 'after insert' trigger sees these changes, but the FEDERATED table's 'after insert' trigger does not. It only sees any alterations made by the FEDERATED table's trigger.
So I can summarize my testing of before and after insert triggers by concluding that information flows during an insert into a FEDERATED table from the server with the FEDERATED table to the server with the base table, but not vice versa.