【PostgreSQL-9.6.3】事件触发器

当预定的事件发生时，事件触发器就会被触发。由于事件触发器设计的权限比较大，所以只有超级用户才能创建和修改触发器。

1. 事件触发器支持的事件分三类：ddl_command_start, ddl_command_end 和 sql_drop。

（1）ddl_command_start：在DDL开始前触发；

（2）ddl_command_end：在DDl结束后触发；

（3）sql_drop：删除一个数据库对象前被触发，其中删除的数据库对象详细信息，可以通过pg_event_trigger_dropped_objects()函数记录下来。

pg_event_trigger_dropped_objects()函数返回的结果集

列名称	列类型	列描述
classid	Oid	对象所在目录的Oid
objjd	Oid	数据库对象的Oid
objsubid	int32	数据库对象的子对象 （如：列）
object_type	text	数据库对象的类型
schema_name	text	数据库对象的模式名
object_name	text	数据库对象的名称
object_identify	text	数据库对象的标识符

2. 各种DDL操作会触发的事件列表：

命令标记	ddl_command_start	ddl_command_end	sql_drop
ALTER AGGREGATE	X	X	-
ALTER COLLATION	X	X	-
ALTER CONVERSION	X	X	-
ALTER DOMAIN	X	X	-
ALTER EXTENSION	X	X	-
ALTER FOREIGN DATA WRAPPER	X	X	-
ALTER FOREIGN TABLE	X	X	X
ALTER FUNCTION	X	X	-
ALTER LANGUAGE	X	X	-
ALTER OPERATOR	X	X	-
ALTER OPERATOR CLASS	X	X	-
ALTER OPERATOR FAMILY	X	X	-
ALTER SCHEMA	X	X	-
ALTER SEQUENCE	X	X	-
ALTER SERVER	X	X	-
ALTER TABLE	X	X	X
ALTER TEXT SEARCH CONFIGURATION	X	X	-
ALTER TEXT SEARCH DICTIONARY	X	X	-
ALTER TEXT SEARCH PARSER	X	X	-
ALTER TEXT SEARCH TEMPLATE	X	X	-
ALTER TRIGGER	X	X	-
ALTER TYPE	X	X	-
ALTER USER MAPPING	X	X	-
ALTER VIEW	X	X	-
CREATE AGGREGATE	X	X	-
CREATE CAST	X	X	-
CREATE COLLATION	X	X	-
CREATE CONVERSION	X	X	-
CREATE DOMAIN	X	X	-
CREATE EXTENSION	X	X	-
CREATE FOREIGN DATA WRAPPER	X	X	-
CREATE FOREIGN TABLE	X	X	-
CREATE FUNCTION	X	X	-
CREATE INDEX	X	X	-
CREATE LANGUAGE	X	X	-
CREATE OPERATOR	X	X	-
CREATE OPERATOR CLASS	X	X	-
CREATE OPERATOR FAMILY	X	X	-
CREATE RULE	X	X	-
CREATE SCHEMA	X	X	-
CREATE SEQUENCE	X	X	-
CREATE SERVER	X	X	-
CREATE TABLE	X	X	-
CREATE TABLE AS	X	X	-
CREATE TEXT SEARCH CONFIGURATION	X	X	-
CREATE TEXT SEARCH DICTIONARY	X	X	-
CREATE TEXT SEARCH PARSER	X	X	-
CREATE TEXT SEARCH TEMPLATE	X	X	-
CREATE TRIGGER	X	X	-
CREATE TYPE	X	X	-
CREATE USER MAPPING	X	X	-
CREATE VIEW	X	X	-
DROP AGGREGATE	X	X	X
DROP CAST	X	X	X
DROP COLLATION	X	X	X
DROP CONVERSION	X	X	X
DROP DOMAIN	X	X	X
DROP EXTENSION	X	X	X
DROP FOREIGN DATA WRAPPER	X	X	X
DROP FOREIGN TABLE	X	X	X
DROP FUNCTION	X	X	X
DROP INDEX	X	X	X
DROP LANGUAGE	X	X	X
DROP OPERATOR	X	X	X
DROP OPERATOR CLASS	X	X	X
DROP OPERATOR FAMILY	X	X	X
DROP OWNED	X	X	X
DROP RULE	X	X	X
DROP SCHEMA	X	X	X
DROP SEQUENCE	X	X	X
DROP SERVER	X	X	X
DROP TABLE	X	X	X
DROP TEXT SEARCH CONFIGURATION	X	X	X
DROP TEXT SEARCH DICTIONARY	X	X	X
DROP TEXT SEARCH PARSER	X	X	X
DROP TEXT SEARCH TEMPLATE	X	X	X
DROP TRIGGER	X	X	X
DROP TYPE	X	X	X
DROP USER MAPPING	X	X	X
DROP VIEW	X	X	X
SELECT INTO	X	X	-

3.  创建事件触发器的语法

CREATE EVENT TRIGGER name

ON EVENT

[ WHEN filter_variable IN ( filter_value [ , ... ]) [ AND ... ] ]

EXECUTE PROCEDURE function_name ()

4. 事件触发器示例

（1）禁止所有DDL操作

--创建触发器函数
create or replace function abort_any_command()
returns event_trigger
language plpgsql
as $$
begin
raise exception 'command % is disabled ',tg_tag;
end;
$$;

--创建触发器
create event trigger abort_ddl on ddl_command_start
execute procedure abort_any_command();

--测试触发器
test=# drop table emp;
ERROR:  command DROP TABLE is disabled
CONTEXT:  PL/pgSQL function abort_any_command() line 3 at RAISE
test=# create table emp01 (x int);
ERROR:  command CREATE TABLE is disabled
CONTEXT:  PL/pgSQL function abort_any_command() line 3 at RAISE

test=# truncate table emp;  --注意：truncate是在普通触发器中触发，在事件触发器中不会触发。
TRUNCATE TABLE

--恢复DDL正常操作

test=# alter event trigger abort_ddl disable;
ALTER EVENT TRIGGER

（2）审计记录所有drop操作

--创建审计记录表
create table log_drop_objects(
op_time         timestamp, --操作执行时间
ddl_tag         text,  --执行的ddl操作
classid         Oid,
objid           Oid,
objsubid        OID,
object_type     text,
schema_name     text,
object_name     text,
object_identify text
);

--创建触发器函数
create function event_trigger_log_drops()
returns event_trigger language plpgsql as $$
declare
obj record;
begin
insert into log_drop_objects select now(),tg_tag,classid,objid,objsubid,
object_type,schema_name,object_name,
object_identity from pg_event_trigger_dropped_objects();
end
$$;

--创建触发器
create event trigger event_trigger_log_drops
on sql_drop
execute procedure event_trigger_log_drops();

--测试触发器
test=# alter table emp drop column salary;
ALTER TABLE
test=#
test=# select ddl_tag,object_type,object_name,object_identity from log_drop_objects;
   ddl_tag   | object_type  | object_name |  object_identity
-------------+--------------+-------------+-------------------
 ALTER TABLE | table column |             | public.emp.salary
(1 row)

test=#
test=# drop table emp;
DROP TABLE
test=#
test=# select ddl_tag,object_type,object_name,object_identity from log_drop_objects;
   ddl_tag   | object_type  |     object_name      |        object_identity
-------------+--------------+----------------------+-------------------------------
 ALTER TABLE | table column |                      | public.emp.salary
 DROP TABLE  | table        | emp                  | public.emp
 DROP TABLE  | type         | emp                  | public.emp
 DROP TABLE  | type         | _emp                 | public.emp[]
 DROP TABLE  | toast table  | pg_toast_16461       | pg_toast.pg_toast_16461
 DROP TABLE  | index        | pg_toast_16461_index | pg_toast.pg_toast_16461_index
 DROP TABLE  | type         | pg_toast_16461       | pg_toast.pg_toast_16461
 DROP TABLE  | trigger      |                      | emp_audit on public.emp
(8 rows)

5. 修改事件触发器

ALTER EVENT TRIGGER name DISABLE
ALTER EVENT TRIGGER name ENABLE [ REPLICA | ALWAYS ]
ALTER EVENT TRIGGER name OWNER TO new_owner
ALTER EVENT TRIGGER name RENAME TO new_name

The End！

2017-08-20