Creating a Database

The first test to see whether you can access the database server is to try to create a database. A running PostgreSQL server can manage many databases. Typically, a separate database is used for each project or for each user.

Your site administrator might have already created a database for your use. He should have told you what the name of your database is. In this case you can omit this step and skip ahead to the next section.

To create a new database, in this example named mydb, you use the following command:

$ createdb mydb

Running this command should produce the following output:

CREATE DATABASE

If you see this output, you may skip over the remainder of this section.

Another response could be similar to this:

psql: could not connect to server: Connection refused Is the server running locally and accepting connections on Unix domain socket "/tmp/.s.PGSQL.5432"? createdb: database creation failed

This means that either the server was not started or it was not started where createdb expected it. Check the installation instructions or consult the administrator.

If you do not have the privileges required to create a database, you will see the following:

ERROR: CREATE DATABASE: permission denied createdb: database creation failed

Not every user has authorization to create new databases. If PostgreSQL refuses to create databases for you then the site administrator needs to grant you permission to create databases. Consult your site administrator if this occurs. If you installed PostgreSQL yourself then you should log in for the purposes of this tutorial under the user account that you started the server as. [1]

You can also create databases with other names. PostgreSQL allows you to create any number of databases at a given site. Database names must have an alphabetic first character and are limited to 31 characters in length. A convenient choice is to create a database with the same name as your current user name. Many tools assume that database name as the default, so it can save you some typing. To create that database, simply type:

$ createdb

You can remove a database if you do not want to use it anymore. For example, if you are the owner (creator) of the database mydb, you can destroy it using the following command:

$ dropdb mydb

For this command, the database name does not default to the user account name—you always need to specify it. Removing a database physically removes all files associated with the database and cannot be undone, so this should only be done with a great deal of forethought.