---
title: "Event Trigger Functions"
id: functions-event-triggers
pg_version: "20devel"
---

<a id="functions-event-triggers"></a>

## 9.31. Event Trigger Functions

PostgreSQL provides these helper functions to retrieve information from event triggers. 

For more information about event triggers, see [Chapter 38](event-triggers.md). 

<a id="pg-event-trigger-ddl-command-end-functions"></a>

### 9.31.1. Capturing Changes at Command End

```
pg_event_trigger_ddl_commands () setof record
```

`pg_event_trigger_ddl_commands` returns a list of DDL commands executed by each user action, when invoked in a function attached to a `ddl_command_end` event trigger. If called in any other context, an error is raised. `pg_event_trigger_ddl_commands` returns one row for each base command executed; some commands that are a single SQL sentence may return more than one row. This function returns the following columns: | Name | Type | Description | 
| --- | --- | --- |
| `classid` | `oid` | OID of catalog the object belongs in | 
| `objid` | `oid` | OID of the object itself | 
| `objsubid` | `integer` | Sub-object ID (e.g., attribute number for a column) | 
| `command_tag` | `text` | Command tag | 
| `object_type` | `text` | Type of the object | 
| `schema_name` | `text` | Name of the schema the object belongs in, if any; otherwise `NULL`. No quoting is applied. | 
| `object_identity` | `text` | Text rendering of the object identity, schema-qualified. Each identifier included in the identity is quoted if necessary. | 
| `in_extension` | `boolean` | True if the command is part of an extension script | 
| `command` | `pg_ddl_command` | A complete representation of the command, in internal format. This cannot be output directly, but it can be passed to other functions to obtain different pieces of information about the command. | 

 

<a id="pg-event-trigger-sql-drop-functions"></a>

### 9.31.2. Processing Objects Dropped by a DDL Command

```
pg_event_trigger_dropped_objects () setof record
```

`pg_event_trigger_dropped_objects` returns a list of all objects dropped by the command in whose `sql_drop` event it is called. If called in any other context, an error is raised. This function returns the following columns: | Name | Type | Description | 
| --- | --- | --- |
| `classid` | `oid` | OID of catalog the object belonged in | 
| `objid` | `oid` | OID of the object itself | 
| `objsubid` | `integer` | Sub-object ID (e.g., attribute number for a column) | 
| `original` | `boolean` | True if this was one of the root object(s) of the deletion | 
| `normal` | `boolean` | True if there was a normal dependency relationship in the dependency graph leading to this object | 
| `is_temporary` | `boolean` | True if this was a temporary object | 
| `object_type` | `text` | Type of the object | 
| `schema_name` | `text` | Name of the schema the object belonged in, if any; otherwise `NULL`. No quoting is applied. | 
| `object_name` | `text` | Name of the object, if the combination of schema and name can be used as a unique identifier for the object; otherwise `NULL`. No quoting is applied, and name is never schema-qualified. | 
| `object_identity` | `text` | Text rendering of the object identity, schema-qualified. Each identifier included in the identity is quoted if necessary. | 
| `address_names` | `text[]` | An array that, together with `object_type` and `address_args`, can be used by the `pg_get_object_address` function to recreate the object address in a remote server containing an identically named object of the same kind. | 
| `address_args` | `text[]` | Complement for `address_names` | 

 

The `pg_event_trigger_dropped_objects` function can be used in an event trigger like this: 
CREATE FUNCTION test_event_trigger_for_drops()
        RETURNS event_trigger LANGUAGE plpgsql AS $$
DECLARE
    obj record;
BEGIN
    FOR obj IN SELECT * FROM pg_event_trigger_dropped_objects()
    LOOP
        RAISE NOTICE '% dropped object: % %.% %',
                     tg_tag,
                     obj.object_type,
                     obj.schema_name,
                     obj.object_name,
                     obj.object_identity;
    END LOOP;
END;
$$;
CREATE EVENT TRIGGER test_event_trigger_for_drops
   ON sql_drop
   EXECUTE FUNCTION test_event_trigger_for_drops();
 

<a id="pg-event-trigger-table-rewrite-functions"></a>

### 9.31.3. Handling a Table Rewrite Event

The functions shown in [Table 9.114](functions-event-triggers.md#functions-event-trigger-table-rewrite) provide information about a table for which a `table_rewrite` event has just been called. If called in any other context, an error is raised. 

<a id="functions-event-trigger-table-rewrite"></a>

**Table Rewrite Information Functions**

| Function | Description | 
| --- | --- |
| `pg_event_trigger_table_rewrite_oid` () → oid | Returns the OID of the table about to be rewritten. |  |
| `pg_event_trigger_table_rewrite_reason` () → integer | Returns a code explaining the reason(s) for rewriting. The value is a bitmap built from the following values: `1` (the table has changed its persistence), `2` (default value of a column has changed), `4` (a column has a new data type) and `8` (the table access method has changed). |  |

These functions can be used in an event trigger like this: 
CREATE FUNCTION test_event_trigger_table_rewrite_oid()
 RETURNS event_trigger
 LANGUAGE plpgsql AS
$$
BEGIN
  RAISE NOTICE 'rewriting table % for reason %',
                pg_event_trigger_table_rewrite_oid()::regclass,
                pg_event_trigger_table_rewrite_reason();
END;
$$;

CREATE EVENT TRIGGER test_table_rewrite_oid
                  ON table_rewrite
   EXECUTE FUNCTION test_event_trigger_table_rewrite_oid();