With no arguments, this function initializes (reinitializes if a connection
had been previously set up) a connection to the Postgres backend.
Since Postgres requires a database to be selected, it will try
to connect to the default database. The connection may fail however for a
variety of reasons, in this case the most likely of all is because
you don't have enough authority to connect to that database.
So use of this particular syntax is discouraged.
The host argument can have the syntax "hostname" or "hostname:portname".
This allows to specify the TCP/IP port to connect to. If it is 0 or "", it
will try to connect to localhost, default port.
The database argument specifies the database to connect to. If 0 or "", it
will try to connect to the specified database.
The username and password arguments are silently ignored, since the Postgres
C API doesn't allow to connect to the server as any user different than the
user running the interface.