How to grant select on a view ... based on IP adress? I wonder if it's possible to allow a client A to "see" some data in a view while allowing any other clients, namely B and C, to see ALL data from the same view.

The distinction between A, B and C would rely on their IP address.
You could use the session information function inet_client_addr(), with limited reach. It reports the IP the server is receiving the current connection from. This is only useful with direct connections to the database, though.

As proof of concept:

SELECT CASE WHEN inet_client_addr() &lt;&lt; '192.168.1.32/30'::inet
         THEN 'foo'
         ELSE 'bar'
       END AS odd_column


&lt;&lt;.. "is contained within" operator.

As @Craig mentioned in a comment, consider the security_barrier option for a view like that:

CREATE VIEW my_odd_view WITH (security_barrier) AS ...


Details in the manual here and here.

The whole idea is rather dubious, though. The proper way would be to use distinct roles and distinct views with grants only for privileged roles.