> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify-poc.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Automate tasks with triggers

> Use PostgreSQL triggers to automatically execute functions when data changes occur. Learn how to create triggers on TimescaleDB hypertables

export const CHUNK = 'chunk';

export const HYPERTABLE = 'hypertable';

export const PG = 'Postgres';

export const TIMESCALE_DB = 'TimescaleDB';

Triggers are special {PG} functions that automatically execute when specific events occur on a table, such as inserts,
updates, or deletes. They enable you to automate tasks like data validation, audit logging, maintaining derived data,
or enforcing complex business rules without requiring application-level code.

Common use cases for triggers include:

* **Data validation**: Enforce complex validation rules beyond what constraints can provide
* **Audit logging**: Automatically track changes to sensitive data
* **Derived data**: Maintain summary tables or denormalized data in sync
* **Error handling**: Capture and route problematic data to separate tables for analysis
* **Notifications**: Send alerts or update external systems when data changes

{TIMESCALE_DB} supports the full range of {PG} triggers. Creating, altering, or dropping triggers on a {HYPERTABLE}
propagates the changes to all of the underlying {CHUNK}s.

## 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.

<Steps>
  <Step title="Create a function that inserts erroneous data into the error_conditions table">
    ```sql theme={"dark"}
    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;
    ```
  </Step>

  <Step title="Create a trigger that calls this function whenever a new row is inserted into the hypertable">
    ```sql theme={"dark"}
    CREATE TRIGGER record_error
      BEFORE INSERT ON conditions
      FOR EACH ROW
      EXECUTE PROCEDURE record_error();
    ```
  </Step>

  <Step title="Verify the trigger works">
    All data is inserted into the `conditions` table, but rows that contain errors are also added to the
    `error_conditions` table.
  </Step>
</Steps>

{TIMESCALE_DB} supports the full range of triggers, including `BEFORE INSERT`, `AFTER INSERT`, `BEFORE UPDATE`,
`AFTER UPDATE`, `BEFORE DELETE`, and `AFTER DELETE`. For more information, see the [{PG} docs][postgres-createtrigger].

[postgres-createtrigger]: https://www.postgresql.org/docs/current/sql-createtrigger.html