Triggers#

What is a Trigger?#

Triggers are SQL statements you can set to run every time a row is inserted, updated, or deleted from a particular table. Triggers receive the value of the row being inserted, updated, or deleted like a parameter, and can change it in some cases.

Database users create triggers. Triggers are schema. Triggers are stored along with other schema elements in the database.

How to use Triggers#

Triggers are a general tool, but they are most commonly used to enforce complex constraints that can’t be expressed by foreign keys, nullness, types, or the check syntax.

Doltgres supports row-level triggers. As in Postgres, you first define a trigger function, usually in PL/pgSQL, and then attach it to a table with CREATE TRIGGER ... BEFORE | AFTER INSERT | UPDATE | DELETE ... FOR EACH ROW EXECUTE FUNCTION ....

Some Postgres trigger features are not yet supported: constraint triggers, DEFERRABLE, REFERENCING, statement-level triggers (FOR EACH STATEMENT), INSTEAD OF triggers, UPDATE OF <columns>, and TRUNCATE events.

Interaction with Doltgres Version Control#

Triggers are versioned in storage like other schema elements. You add and commit trigger changes just like any other schema change. Note that unlike views, triggers do not appear in the dolt_schemas table.