create function problem

I've used the following sql to create the function and
function creation is also successful.

create function usage(text)
returns numeric
as 'select ceil(sum(sessiontime)/60) from ath_online
where loginname=\'$1\' and  startdate >= (select
startdate from cst_package where status=\'t\' and
cid=(select cid from cst_customer where
loginname=\'$1\'));'
language 'sql';

executing this function as 
select usage('kancha');

returns no records. while executing the query directly
replacke $1 with kancha returns result. Where did i go
wrong ??

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