PostgreSQL - Tipps und Tricks: Unterschied zwischen den Versionen

Version vom 13. November 2012, 00:22 Uhr

Siehe auch:

• PostgreSQL, PostgreSQL optimieren und PostgreSQL-Datentyp hstore
• PostGIS und PostGIS - Tipps und Tricks

Stefan's Notizen...

Passwörter

• Setzen/Ändern Passwort für eine Datenbank:

 % psql -d unsere_db -c "ALTER USER unsere_db WITH PASSWORD 'neues_passwort';"

• TIPP: PG Programme haben nicht gern, wenn das PW fehlt!

• TIPP: Das Setzen des Passworts für Super User postgres auf PW postgres verlangt template1 und nicht postgres:

 % psql -d template1 -c "ALTER USER postgres WITH PASSWORD 'postgres';"

• psql und wohl alle weiteren PostgreSQL-Tools (dropdb, createdb, pg_dump, etc.) u.a. brauchen Angaben zu Benutzer und Passwort. Der Benutzer wird mit Parameter -U mitgegeben, das Passwort hingegen kann (mit Absicht) nicht mitgegeben werden. Es gibt aber die Möglichkeit, Umgebungsvariablen zu setzen:

 SET PGUSER=postgres
 SET PGPASSWORD=<meinpasswort>

• Start pgsl-Client mit Umlauten (Windows):

 > cmd /c chcp 1252
 > psql -d gisdb -U postgres
 postgres=# SET CLIENT_ENCODING TO 'LATIN1';
 postgres=# <do whatever you must do in psql...>
 > cmd /c chcp 850

Create "Read-only User"

From: [1]

If you only grant CONNECT to a database, the user can connect but has no other privileges. In PostgreSQL 8.x you have to grant USAGE on namespaces (schemas) and SELECT on tables and views individually. So something like:

 GRANT CONNECT ON DATABASE mydb TO xxx;
 -- This assumes you're actually connected to mydb..
 GRANT USAGE ON SCHEMA public TO xxx;
 GRANT SELECT ON mytable TO xxx;

Granting 'SELECT' to each table/view individually can be a bore. Something like this can help:

 SELECT 'GRANT SELECT ON ' || relname || ' TO xxx;'
 FROM pg_class JOIN pg_namespace ON pg_namespace.oid = pg_class.relnamespace
 WHERE nspname = 'public' AND relkind IN ('r', 'v')

This should output the relevant GRANT commands to GRANT SELECT on all tables and views in public, for copy-n-paste.

PostgreSQL 9:

In PostgreSQL 9.0 its easier. You still need to grant USAGE permissions on schemas, but you can grant permissions on all tables, views etc. in the schema using a single command rather than having to generate them:

 GRANT SELECT ON ALL TABLES IN SCHEMA public TO xxx;

This only affects tables that have already been created, so it's the equivalent of the generated commands above. More powerfully, you can automatically have default roles assigned to new objects in future:

 ALTER DEFAULT PRIVILEGES IN SCHEMA public
    GRANT SELECT ON TABLES TO osmgis;

Note that by default this will only affect objects (tables) created by the user that issued this command: although it can also be set on any role that the issuing user is a member of. However, you don't pick up default privileges for all roles you're a member of when creating new objects... so there's still some faffing around. If you adopt the approach that a database has an owning role, and schema changes are performed as that owning role, then you should assign default privileges to that owning role. IMHO this is all a bit confusing and you may need to experiment to come up with a functional workflow.

Daten laden/importieren

Siehe http://wiki.postgresql.org/wiki/COPY

COPY Syntax:

• Tab-Delimited

 COPY geometry_columns (f_table_catalog, f_table_schema, f_table_name, f_geometry_column, coord_dimension, srid, type) FROM stdin;
 catalog	public	planet_osm_point	way	2	900913	POINT
 catalog	public	planet_osm_line	way	2	900913	LINESTRING
 \.

Foreign Data Wrappers

Ab Version 9.1 werden Foreign Data Wrappers (FDW) und ein Teil des SQL/MED-Standards unterstützt.

file_fdw ist eine offizielle Extension (contrib module): [2].

Siehe auch PostgreSQL Wiki:

• Foreign_data_wrappers [3]
• SQL/MED [4]

PostgreSQL SQL

Siehe auch im Wiki der Vorlesung Datenbanken (Dbs1) von Prof. S. Keller.

Version:

 select version();

Anfrage des Geometrie-Typs ('the_geom' ist der Name des Geometrie-Felds):

 SELECT *
   FROM sometable
   WHERE GeometryType(the_geom) = 'GEOMETRYCOLLECTION'

Problem mit Datenfelder (for < 8.3):

 SELECT the_geom ... (end_date - NOW() >= 10) AS GREEN 
   AND (end_date - NOW() < 0) AS RED ... FROM ...

Casting changes in >= 8.3:

 SELECT the_geom ... (end_date - NOW() >= '10 DAYS'::INTERVAL) AS GREEN 
   AND (end_date - NOW() < '0'::INTERVAL) AS RED ... FROM ...

 SELECT the_geom ...
   EXTRACT(DAY FROM (end_date - NOW()) >= 10) AS GREEN
   AND EXTRACT(DAY FROM (end_date - NOW()) < 0) AS RED ... FROM ...

hstore

Stichworte: Key-Value-Attributes, Hashtable, nosql-Database.

Siehe auch:

• PostgreSQL docs.
• Seminar thesis from M. Ott about "Key/Value Pair Versus hstore - Benchmarking Entity-Attribute-Value Structures in PostgreSQL" in [5]
• Beispiele: PostGIS Terminal.

Binary Large Objects (LOB, BLOB)

Siehe PostgreSQL - Binary Large Objects.

Data Warehousing mit PostgreSQL

Stichworte: PostgreSQL-Module cube, PostgreSQL-Module tablefunc (mit crosstab).

tbd.

Konfiguration

Die pg_hba.conf kann so eingestellt werden, dass bei der Ausführung von PostgreSQL-Kommandozeilen-Tools kein Passwort übertragen werden muss.

Bsp mit 127.0.0.1: Anstelle

 # IPv4 local connections:
 host    all         all         127.0.0.1/32          md5

neu:

 # IPv4 local connections:
 host    all         all         127.0.0.1/32          trust

Backup und Restore

Tipps:

• Dont't store data in schema 'public' for several reasons. One is, that until PG 8, all db additional objects (functions, triggers) are maintainted in schema public.
• Eventually switch off Privileges. See also Tab „Dump Options #1“ > Don’t Save Privilege in pgAdmin3.

Doku.:

• 'PostgreSQL 9.0 pg_dump, pg_dumpall, pg_restore cheatsheet' from postgresonline.com.
• PostGIS Hard Upgrade
• PostgreSQL Chapter 24. Backup and Restore

# Backup full database
pg_dump -h host -U user -W database > backup.sql

# Restore full database
psql -d database -f backup.sql

# Backup database schema
pg_dump -sv prueba -O > backup.schema.sql

# Backup database data
pg_dump -Fc -f backup.data.dump -a --disable-triggers database

Weitere Tipps...

Code snippets auf Postgres Wiki

Convert text to number

See [6]

SQL MERGE/UPSERT Command

The PostgreSQL documentation provides a solution for an MERGE/INSERT function. 'UPSERT' is the PostgreSQL slang for ANSI SQL 'Merge' and means UPDATE-SELECT. But this solution proposal hast concurrency issues which have been avoided by this proposal (by Depesz's Blog [7]).

PL/pgSQL-Funktion für ein MERGE/UPSERT mit einem Attribut ('in_whatever'):

 -- All function parameters and all the update and insert 
 -- statements in the body need to be adapted for specific tables
 CREATE OR REPLACE FUNCTION merge_db( key INT, data TEXT ) 
 RETURNS void AS $$
 BEGIN
     -- first try to update with primary key as id
     UPDATE db SET b=data WHERE a = key;
     --UPDATE db SET b=data,etc. WHERE a = key;
     IF FOUND THEN
         RETURN;
     END IF;
     -- not there, so try to insert the key
     -- if someone else inserts the same key
     BEGIN
         INSERT INTO db (a,b) VALUES (key, data);
         --INSERT INTO db (a,b,etc.) VALUES (a,b,etc.);
     EXCEPTION WHEN OTHERS THEN
         -- try another time
         UPDATE db SET b=data WHERE a = key;
     END;
     RETURN;
 END;
 $$ LANGUAGE plpgsql;

Unfortunately, there's no other generic function around which would accept any table structure.

Triggers

Tipps:

• Prefer triggers over rules (since 9.0).
• ...

Q: Is there a restriction that an insert trigger can't modify own or other rows of the table that fired it?
A: There's no such restriction. The best way to change the inserted row is to do it before the insertion, though. Trying to modify the inserted row can have slightly strange effects.