Svarbu

Vertimas yra bendruomenės pastangos, prie kurių jūs galite prisijungti. Šis puslapis šiuo metu išverstas 26.67%.

15.6. Pamoka: taisyklės

Taisyklės leidžia perrašyti įeinančios „užklausos medį“. Vienas dažnas naudojimas yra sukurti vaizdus, įskaitant ir keičiamus vaizdus. - Wikipedia

Šios pamokos tikslas: išmokti kurti naujas duomenų bazės taisykles.

15.6.1. Creating a logging rule

Say you want to log every change of phone_no in your people table in to a people_log table. So you set up a new table:

create table people_log (name text, time timestamp default NOW());

In the next step, create a rule that logs every change of a phone_no in the people table into the people_log table:

create rule people_log as on update to people
  where NEW.phone_no <> OLD.phone_no
  do insert into people_log values (OLD.name);

To test that the rule works, let’s modify a phone number:

update people set phone_no = '082 555 1234' where id = 2;

Check that the people table was updated correctly:

select * from people where id=2;

 id |    name    | house_no | street_id |   phone_no
----+------------+----------+-----------+--------------
  2 | Joe Bloggs |        3 |         2 | 082 555 1234
(1 row)

Now, thanks to the rule we created, the people_log table will look like this:

select * from people_log;

    name    |            time
------------+----------------------------
 Joe Bloggs | 2014-01-11 14:15:11.953141
(1 row)

Pastaba

The value of the time field will depend on the current date and time.

15.6.2. In Conclusion

Rules allow you to automatically add or change data in your database to reflect changes in other parts of the database.

15.6.3. What’s Next?

The next module will introduce you to Spatial Database using PostgreSQL with PostGIS extension, which takes these database concepts and applies them to GIS data.