以Postgres10为例：
如下教程需要先安装这个组件：yum install postgresql10-contrib
安装完成后，然后，登录到pgsql，执行如下的一系列命令(以要审计db1为例)：
postgres=# create database db1 ;
postgres=# \c db1 ;
db1=# create extension hstore;
db1=# create or replace function ef_alter() returns event_trigger as $$
declare
rec hstore;
begin
select hstore(pg_stat_activity.*) into rec from pg_stat_activity where pid=pg_backend_pid(); -- 记录pg_stat_activity的内容
insert into aud_alter (ctx) values (rec);
end;
$$ language plpgsql strict;
db1=# create event trigger e_alter on ddl_command_end when tag in ('ALTER TABLE') execute procedure ef_alter();
db1=# create table aud_alter(id serial primary key,crt_time timestamp default now(),ctx hstore);
### 测试
db1=# create table test(id int);
db1=# alter table test alter column id type int8;
db1=# \x;
db1=# select * from aud_alter;
-[ RECORD 1 ]-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
id | 1
crt_time | 2018-07-29 13:20:14.783321
ctx | "pid"=>"32512","datid"=>"16386","query"=>"alter table test alter column id type int8;","state"=>"active","datname"=>"db1","usename"=>"postgres","usesysid"=>"10","wait_event"=>NULL,"xact_start"=>"2018-07-29 13:40:12.142124+08","backend_xid"=>"698","client_addr"=>NULL,"client_port"=>"-1","query_start"=>"2018-07-29 13:40:12.142124+08","backend_type"=>"client backend","backend_xmin"=>"698","state_change"=>"2018-07-29 13:40:12.142128+08","backend_start"=>"2018-07-29 13:38:50.710944+08","client_hostname"=>NULL,"wait_event_type"=>NULL,"application_name"=>"psql"
db1=# \x;
db1=# select each(ctx) from aud_alter where id=1;
each
-------------------------------------------------------
(pid,32512)
(datid,16386)
(query,"alter table test alter column id type int8;")
(state,active)
(datname,db1)
(usename,postgres)
(usesysid,10)
(wait_event,)
(xact_start,"2018-07-29 13:40:12.142124+08")
(backend_xid,698)
(client_addr,)
(client_port,-1)
(query_start,"2018-07-29 13:40:12.142124+08")
(backend_type,"client backend")
(backend_xmin,698)
(state_change,"2018-07-29 13:40:12.142128+08")
(backend_start,"2018-07-29 13:38:50.710944+08")
(client_hostname,)
(wait_event_type,)
(application_name,psql)
(20 rows)
