为什么我使用这些 postgresql 时态数据库模式和查询得到重复的行？
Why am I getting duplicate rows with these postgresql temporal db schema & queries?
我正在关注一些关于在 postgresql 中设置时态数据库的信息。首先是问题，然后是技术位。
问题：当我在 public.countries table 中执行一次干净的插入时，为什么我在 temporal.countries table 中得到了双行？我只看到一个插入（在 countries_ins 规则中）。这是功能还是错误？
好的，现在架构：
DROP SCHEMA IF EXISTS temporal CASCADE;
DROP SCHEMA IF EXISTS history CASCADE;
----------------------------
-- Temporal countries schema
-- vjt@openssl.it
--
create schema temporal; -- schema containing all temporal tables
create schema history; -- schema containing all history tables
-- Current countries data - nothing special
--
create table temporal.countries (
id serial primary key,
name varchar UNIQUE
);
-- Countries historical data.
--
-- Inheritance is used to avoid duplicating the schema from the main table.
-- Please note that columns on the main table cannot be dropped, and other caveats
-- http://www.postgresql.org/docs/9.0/static/ddl-inherit.html#DDL-INHERIT-CAVEATS
--
create table history.countries (
hid serial primary key,
valid_from timestamp not null,
valid_to timestamp not null default '9999-12-31',
recorded_at timestamp not null default now(),
constraint from_before_to check (valid_from < valid_to),
constraint overlapping_times exclude using gist (
box(
point( extract( epoch from valid_from), id ),
point( extract( epoch from valid_to - interval '1 millisecond'), id )
) with &&
)
) inherits ( temporal.countries );
create index timestamps on history.countries using btree ( valid_from, valid_to ) with ( fillfactor = 100 );
create index country_id on history.countries using btree ( id ) with ( fillfactor = 90 );
-- The countries view, what the Rails' application ORM will actually CRUD on, and
-- the core of the temporal updates.
--
-- SELECT - return only current data
--
create view public.countries as select * from only temporal.countries;
-- INSERT - insert data both in the current data table and in the history table
--
create rule countries_ins as on insert to public.countries do instead (
insert into temporal.countries ( name )
values ( new.name )
returning temporal.countries.*;
insert into history.countries ( id, name, valid_from )
values ( currval('temporal.countries_id_seq'), new.name, now() )
);
-- UPDATE - set the last history entry validity to now, save the current data in
-- a new history entry and update the current table with the new data.
--
create rule countries_upd as on update to countries do instead (
update history.countries
set valid_to = now()
where id = old.id and valid_to = '9999-12-31';
insert into history.countries ( id, name, valid_from )
values ( old.id, new.name, now() );
update only temporal.countries
set name = new.name
where id = old.id
);
-- DELETE - save the current data in the history and eventually delete the data
-- from the current table.
--
create rule countries_del as on delete to countries do instead (
update history.countries
set valid_to = now()
where id = old.id and valid_to = '9999-12-31';
delete from only temporal.countries
where temporal.countries.id = old.id
);
-- EOF
当我将它加载到一个空白数据库中并执行一次插入时，会发生以下情况（请查看第 39-40 行以了解令人惊讶的（对我来说）结果）。
1 test=# \i /home/username/temporal.sql
2 psql:/home/sirrobert/temporal.sql:1: NOTICE: drop cascades to 3 other objects
3 DETAIL: drop cascades to table temporal.countries
4 drop cascades to view countries
5 drop cascades to table history.countries
6 DROP SCHEMA
7 DROP SCHEMA
8 CREATE SCHEMA
9 CREATE SCHEMA
10 CREATE TABLE
11 CREATE TABLE
12 CREATE INDEX
13 CREATE INDEX
14 CREATE VIEW
15 CREATE RULE
16 CREATE RULE
17 CREATE RULE
18 test=# SELECT * FROM public.countries;
19 id | name
20 ----+------
21 (0 rows)
22
23 test=# SELECT * FROM temporal.countries;
24 id | name
25 ----+------
26 (0 rows)
27
28 test=# INSERT INTO public.countries (name) VALUES ('USA');
29 INSERT 0 1
30 test=# SELECT * FROM public.countries;
31 id | name
32 ----+------
33 1 | USA
34 (1 row)
35
36 test=# SELECT * FROM temporal.countries;
37 id | name
38 ----+------
39 1 | USA
40 1 | USA
41 (2 rows)
您将数据插入到两个表 temporal.countries 和 history.countries 中，后者继承自前者。这是错误的做法。您应该 只 插入 history.countries 和附加属性。当您随后查询 temporal.countries 时，您会看到一条记录，但没有有效的 from/to 信息。
更新记录后，您将获得重复项。您目前的方法无法解决这个问题。但是您实际上并不需要继承。您可以有两个单独的表，然后创建一个视图 public.countries，其中 return 当前有效的行来自 temporal.countries:
create table temporal.countries (
id serial primary key,
name varchar UNIQUE
);
create table history.countries (
hid serial primary key,
<b>country integer not null references temporal.countries,
name varchar,</b>
valid_from timestamp not null,
valid_to timestamp not null default '9999-12-31',
recorded_at timestamp not null default now(),
constraint from_before_to check (valid_from < valid_to),
constraint overlapping_times exclude using gist (
box(
point( extract( epoch from valid_from), id ),
point( extract( epoch from valid_to - interval '1 millisecond'), id )
) with &&
)
) <strike> inherits ( temporal.countries )</strike>;
现在仅创建 return 当前有效国家/地区的视图：
create view public.countries as
select c.*
from temporal.countries c
join history.countries h on h.country = c.id
where localtimestamp between h.valid_from and h.valid_to;
你的三个规则：
-- INSERT - insert data in temporal.countries <b>and metadata in history.countries</b>
create rule countries_ins as on insert to public.countries do instead (
insert into temporal.countries ( name )
values ( new.name )
returning temporal.countries.*;
insert into history.countries ( <b>country</b>, name, valid_from )
values ( currval('temporal.countries_id_seq'), new.name, now() )
);
-- UPDATE - set the last history entry validity to now, save the current data in
-- a new history entry and update the current table with the new data.
create rule countries_upd as on update to countries do instead (
update history.countries
set valid_to = now()
where id = old.id <strike>and valid_to = '9999-12-31'</strike>; -- view shows only valid data
insert into history.countries ( <b>country</b>, name, valid_from )
values ( old.id, new.name, now() );
update <strike>only</strike> temporal.countries
set name = new.name
where id = old.id
);
-- DELETE - save the current date in the history <strike>and eventually delete the data
-- from the current table.</strike>
create rule countries_del as on delete to countries do instead (
update history.countries
set valid_to = LOCALTIMESTAMP
where id = old.id <strike>and valid_to = '9999-12-31'</strike>;
-- don't delete country data, view won't show it anyway
<strike>delete from only temporal.countries
where temporal.countries.id = old.id</strike>
);
我正在关注一些关于在 postgresql 中设置时态数据库的信息。首先是问题，然后是技术位。
问题：当我在 public.countries table 中执行一次干净的插入时，为什么我在 temporal.countries table 中得到了双行？我只看到一个插入（在 countries_ins 规则中）。这是功能还是错误？
好的，现在架构：
DROP SCHEMA IF EXISTS temporal CASCADE;
DROP SCHEMA IF EXISTS history CASCADE;
----------------------------
-- Temporal countries schema
-- vjt@openssl.it
--
create schema temporal; -- schema containing all temporal tables
create schema history; -- schema containing all history tables
-- Current countries data - nothing special
--
create table temporal.countries (
id serial primary key,
name varchar UNIQUE
);
-- Countries historical data.
--
-- Inheritance is used to avoid duplicating the schema from the main table.
-- Please note that columns on the main table cannot be dropped, and other caveats
-- http://www.postgresql.org/docs/9.0/static/ddl-inherit.html#DDL-INHERIT-CAVEATS
--
create table history.countries (
hid serial primary key,
valid_from timestamp not null,
valid_to timestamp not null default '9999-12-31',
recorded_at timestamp not null default now(),
constraint from_before_to check (valid_from < valid_to),
constraint overlapping_times exclude using gist (
box(
point( extract( epoch from valid_from), id ),
point( extract( epoch from valid_to - interval '1 millisecond'), id )
) with &&
)
) inherits ( temporal.countries );
create index timestamps on history.countries using btree ( valid_from, valid_to ) with ( fillfactor = 100 );
create index country_id on history.countries using btree ( id ) with ( fillfactor = 90 );
-- The countries view, what the Rails' application ORM will actually CRUD on, and
-- the core of the temporal updates.
--
-- SELECT - return only current data
--
create view public.countries as select * from only temporal.countries;
-- INSERT - insert data both in the current data table and in the history table
--
create rule countries_ins as on insert to public.countries do instead (
insert into temporal.countries ( name )
values ( new.name )
returning temporal.countries.*;
insert into history.countries ( id, name, valid_from )
values ( currval('temporal.countries_id_seq'), new.name, now() )
);
-- UPDATE - set the last history entry validity to now, save the current data in
-- a new history entry and update the current table with the new data.
--
create rule countries_upd as on update to countries do instead (
update history.countries
set valid_to = now()
where id = old.id and valid_to = '9999-12-31';
insert into history.countries ( id, name, valid_from )
values ( old.id, new.name, now() );
update only temporal.countries
set name = new.name
where id = old.id
);
-- DELETE - save the current data in the history and eventually delete the data
-- from the current table.
--
create rule countries_del as on delete to countries do instead (
update history.countries
set valid_to = now()
where id = old.id and valid_to = '9999-12-31';
delete from only temporal.countries
where temporal.countries.id = old.id
);
-- EOF
当我将它加载到一个空白数据库中并执行一次插入时，会发生以下情况（请查看第 39-40 行以了解令人惊讶的（对我来说）结果）。
1 test=# \i /home/username/temporal.sql
2 psql:/home/sirrobert/temporal.sql:1: NOTICE: drop cascades to 3 other objects
3 DETAIL: drop cascades to table temporal.countries
4 drop cascades to view countries
5 drop cascades to table history.countries
6 DROP SCHEMA
7 DROP SCHEMA
8 CREATE SCHEMA
9 CREATE SCHEMA
10 CREATE TABLE
11 CREATE TABLE
12 CREATE INDEX
13 CREATE INDEX
14 CREATE VIEW
15 CREATE RULE
16 CREATE RULE
17 CREATE RULE
18 test=# SELECT * FROM public.countries;
19 id | name
20 ----+------
21 (0 rows)
22
23 test=# SELECT * FROM temporal.countries;
24 id | name
25 ----+------
26 (0 rows)
27
28 test=# INSERT INTO public.countries (name) VALUES ('USA');
29 INSERT 0 1
30 test=# SELECT * FROM public.countries;
31 id | name
32 ----+------
33 1 | USA
34 (1 row)
35
36 test=# SELECT * FROM temporal.countries;
37 id | name
38 ----+------
39 1 | USA
40 1 | USA
41 (2 rows)
您将数据插入到两个表 temporal.countries 和 history.countries 中，后者继承自前者。这是错误的做法。您应该 只 插入 history.countries 和附加属性。当您随后查询 temporal.countries 时，您会看到一条记录，但没有有效的 from/to 信息。
更新记录后，您将获得重复项。您目前的方法无法解决这个问题。但是您实际上并不需要继承。您可以有两个单独的表，然后创建一个视图 public.countries，其中 return 当前有效的行来自 temporal.countries:
create table temporal.countries (
id serial primary key,
name varchar UNIQUE
);
create table history.countries (
hid serial primary key,
<b>country integer not null references temporal.countries,
name varchar,</b>
valid_from timestamp not null,
valid_to timestamp not null default '9999-12-31',
recorded_at timestamp not null default now(),
constraint from_before_to check (valid_from < valid_to),
constraint overlapping_times exclude using gist (
box(
point( extract( epoch from valid_from), id ),
point( extract( epoch from valid_to - interval '1 millisecond'), id )
) with &&
)
) <strike> inherits ( temporal.countries )</strike>;
现在仅创建 return 当前有效国家/地区的视图：
create view public.countries as
select c.*
from temporal.countries c
join history.countries h on h.country = c.id
where localtimestamp between h.valid_from and h.valid_to;
你的三个规则：
-- INSERT - insert data in temporal.countries <b>and metadata in history.countries</b>
create rule countries_ins as on insert to public.countries do instead (
insert into temporal.countries ( name )
values ( new.name )
returning temporal.countries.*;
insert into history.countries ( <b>country</b>, name, valid_from )
values ( currval('temporal.countries_id_seq'), new.name, now() )
);
-- UPDATE - set the last history entry validity to now, save the current data in
-- a new history entry and update the current table with the new data.
create rule countries_upd as on update to countries do instead (
update history.countries
set valid_to = now()
where id = old.id <strike>and valid_to = '9999-12-31'</strike>; -- view shows only valid data
insert into history.countries ( <b>country</b>, name, valid_from )
values ( old.id, new.name, now() );
update <strike>only</strike> temporal.countries
set name = new.name
where id = old.id
);
-- DELETE - save the current date in the history <strike>and eventually delete the data
-- from the current table.</strike>
create rule countries_del as on delete to countries do instead (
update history.countries
set valid_to = LOCALTIMESTAMP
where id = old.id <strike>and valid_to = '9999-12-31'</strike>;
-- don't delete country data, view won't show it anyway
<strike>delete from only temporal.countries
where temporal.countries.id = old.id</strike>
);