how to use function from different database

Hi,

I created a generic function (DATEFIFF) login to postgres database using psql. ANd I wanted to use across the entire instance , from all other databases.

postgres=> CREATE FUNCTION DateDiff (units VARCHAR(30), start_t TIMESTAMP, end_t TIMESTAMP)
postgres->      RETURNS INT AS $$
postgres$>    DECLARE
postgres$>      diff_interval INTERVAL;

...

...

grant execute on function DATEDIFF to public;

grant execute on function DATEDIFF(varchar,timestamp,timestamp) to public;

I tried both the grant one at a time, none of them works.

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Connected to another database

\c application1

application1=> SELECT * from DATEDIFF('second', '2011-12-30 08:54:55'::timestamp, '2011-12-30 08:56:10'::timestamp);
ERROR:  function datediff(unknown, timestamp without time zone, timestamp without time zone) does not exist
LINE 1: SELECT * from DATEDIFF('second', '2011-12-30 08:54:55'::time...
                      ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
application1=>

How can I use this function across my entire postgresql instance from any databases ?

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