Event Triggers

EVENT TRIGGER declarations that fire on DDL events.

Event triggers are database-level (not cluster-level) and fire on DDL events. They are declared at the top level of a .dpg file (not inside a schema block).

Basic event trigger

EVENT TRIGGER prevent_drop_table
    ON sql_drop
    WHEN TAG IN ('DROP TABLE', 'DROP SCHEMA')
    EXECUTE FUNCTION abort_drop();

-- emits
CREATE EVENT TRIGGER "prevent_drop_table"
    ON sql_drop
    WHEN TAG IN ('DROP TABLE', 'DROP SCHEMA')
    EXECUTE FUNCTION abort_drop();

ddl_command_start trigger

EVENT TRIGGER audit_ddl
    ON ddl_command_start
    EXECUTE FUNCTION log_ddl_start();

-- emits
CREATE EVENT TRIGGER "audit_ddl"
    ON ddl_command_start
    EXECUTE FUNCTION log_ddl_start();

Available events

Event	Fires when
`ddl_command_start`	Before any DDL command executes
`ddl_command_end`	After any DDL command completes
`sql_drop`	Before objects are dropped
`table_rewrite`	Before a table is rewritten
`login` (PostgreSQL 17+)	Once per authenticated connection, before the session’s first query — `WHEN TAG IN (...)` doesn’t apply (no command tag to filter on)

Diffing behaviour

Change	SQL	Safety
New event trigger	`CREATE EVENT TRIGGER`	`SAFE`
Event/`WHEN TAG IN`/function changed	`DROP EVENT TRIGGER` + `CREATE EVENT TRIGGER`	`SAFE` (no data involved)
Enable state changed only	`ALTER EVENT TRIGGER ENABLE/DISABLE` (or `ENABLE REPLICA`/`ENABLE ALWAYS`)	`SAFE`
Owner changed	`ALTER EVENT TRIGGER OWNER TO`	`SAFE`
Renamed (`RENAMED FROM`)	`ALTER EVENT TRIGGER RENAME TO`	`CAUTION`
Removed event trigger	`DROP EVENT TRIGGER`	`SAFE`