I can't connect to a local PostGIS database. My installation is with Mac OS X (10.8), Postgres.app (in doc it's said to have PostGIS included) and Quantum GIS 1.8.
When I want to add a connection to PostgreSQL, I'm specifying name, host (localhost), port (5432), database name, user name and password (service field left empty).
I can connect to a database with Navicat, so database server seems to run correctly.
With the exact information in QGIS used in Navicat, it can't connect... why?
You should verify that you can connect using psql. Try psql -U username -h localhost dbname. It should prompt for a password then connect. Run SELECT postgis_version(); to verify that PostGIS is active in the database.
If you can connect but SELECT postgis_version() reports an error, PostGIS isn't installed in the database:
ERROR: function postgis_version() does not exist
LINE 1: SELECT postgis_version();
Other solution:
SELECT * FROM Postgis_lib_version();
If you want also to see the version of PostGIS and the version number of the libraries GEOS and Proj4 just change lib to Full.
If you get the above error, then presuming you're running PostGIS 2.0 on PostgreSQL 9.1 or above, connect as user postgres and run CREATE EXTENSION postgis;. Eg:
psql -U postgres -h localhost dbname -c 'CREATE EXTENSION postgis;'
You might also need to install some of the extras, like the PostGIS topology support:
CREATE EXTENSION postgis_topology;
or the legacy support script, which isn't packaged as an extension and must be sourced:
psql -U postgres -h localhost dbname -f /path/to/postgis-2.0/legacy.sql
See the PostGIS documentation.
If you can't connect to the DB, it's probably a pg_hba.conf issue, failure to create the DB or user, etc. Hard to say without error messages and log contents.
Ok, in fact, the problem was PostGIS not activated in Postgres.app out of the box. And when we want to CREATE EXTENSION postgis, we have this error:
ERROR: could not load library "/Applications/Postgres.app/Contents/MacOS/lib/rtpostgis-2.0.so": dlopen(/Applications/Postgres.app/Contents/MacOS/lib/rtpostgis-2.0.so, 10): Library not loaded: /usr/local/lib/libjpeg.8.dylib Referenced from: /Applications/Postgres.app/Contents/MacOS/lib/libgdal.dylib Reason: image not found
It's because the file /usr/local/lib/libjpeg.8.dylib is not installed on Mac OS X 10.8 by default. We can install it with MacBrew using brew install libjpeg.
When it's done, we can successfully use the CREATE EXTENSION command, as the previous answer suggests:
psql -U postgres -h localhost dbname -c 'CREATE EXTENSION postgis;'
Note: with Postgres.app, the user postgres doesn't exist by default, you can use any user created with proper privileges, so replace it in previous command.
Et voilà! Quantum GIS can connect to PostgreSQL server.