One connects to a database using the following statement:
EXEC SQL CONNECT TO target [AS connection-name] [USER user-name];
The target can be specified in the following ways:
dbname[@hostname][:port]
tcp:postgresql://hostname[:port][/dbname][?options]
unix:postgresql://hostname[:port][/dbname][?options]
character variable
character string
DEFAULT
There are also different ways to specify the user name:
userid
userid/password
userid IDENTIFIED BY password
userid USING password
The userid and password may be a constant text, a character variable, or a character string.
The connection-name is used to handle multiple connections in one program. It can be omitted if a program uses only one connection.
Read the upstream documentation. For corrections, first check the current version.