Automate tasks with triggers

TimescaleDB supports PostgreSQL triggers on a hypertable the same way you use them on a regular table. When you create, alter, drop, enable, or disable a trigger on a hypertable — including via ALTER TABLE … ENABLE/DISABLE TRIGGER with the ALL, USER, ALWAYS, and REPLICA variants — TimescaleDB propagates the change to every chunk.

Create a trigger

This example creates a new table called error_conditions with the same schema as conditions, but that only stores records which are considered errors. An error, in this case, is when an application sends a temperature or humidity reading with a value that is greater than or equal to 1000.

1. Create a function that inserts erroneous data into the error_conditions table

   CREATE OR REPLACE FUNCTION record_error()
     RETURNS trigger AS $record_error$
   BEGIN
    IF NEW.temperature >= 1000 OR NEW.humidity >= 1000 THEN
      INSERT INTO error_conditions
        VALUES(NEW.time, NEW.location, NEW.temperature, NEW.humidity);
    END IF;
    RETURN NEW;
   END;
   $record_error$ LANGUAGE plpgsql;

2. Create a trigger that calls this function whenever a new row is inserted into the hypertable

   CREATE TRIGGER record_error
     BEFORE INSERT ON conditions
     FOR EACH ROW
     EXECUTE FUNCTION record_error();

3. Verify that error rows are captured

   All data is inserted into the conditions table, but rows that contain errors are also added to the error_conditions table.

For all supported trigger types and clauses, see the PostgreSQL CREATE TRIGGER docs.

Limitations

• Triggers are not supported on continuous aggregates.
• ROW-level triggers with transition tables are not supported on hypertables.
• DELETE triggers with transition tables are not supported.