## 9.29. Event Trigger Functions

[9.29.1. Capturing Changes at Command End](functions-event-triggers.html#PG-EVENT-TRIGGER-DDL-COMMAND-END-FUNCTIONS)

[9.29.2. Processing Objects Dropped by a DDL Command](functions-event-triggers.html#PG-EVENT-TRIGGER-SQL-DROP-FUNCTIONS)

[9.29.3. Handling a Table Rewrite Event](functions-event-triggers.html#PG-EVENT-TRIGGER-TABLE-REWRITE-FUNCTIONS)

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

 For more information about event triggers, see [Chapter 40](event-triggers.html).

### 9.29.1. 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.|

### 9.29.2. 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();

```

### 9.29.3. Handling a Table Rewrite Event

 The functions shown in [Table 9.100](functions-event-triggers.html#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.

**Table 9.100. Table Rewrite Information Functions**

|                                                                          Function<br/><br/> Description                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|                               []() `pg_event_trigger_table_rewrite_oid` () → `oid`<br/><br/> Returns the OID of the table about to be rewritten.                                |
|[]() `pg_event_trigger_table_rewrite_reason` () → `integer`<br/><br/> Returns a code explaining the reason(s) for rewriting. The exact meaning of the codes is release dependent.|

 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();

```

