function doesn't return value

[siva pothireddy]

DROP FUNCTION IF EXISTS fn_GetEligibleBalance;
CREATE FUNCTION 'fn_GetEligibleBalance`(accountId int) RETURNS decimal
BEGIN
declare eligible_balance decimal;

select Balance into eligible_balance
from tb_account_transactions
where Id = (select max(Id) from tb_account_transactions where AccountId = accountId and EligibleDate <= curdate());

return(eligible_balance);
END;

select fn_GetEligibleBalance(3);

I always get 0 as return value though it have value. I get correct value if i ran select part separate. Is there any issue with select into statement inside a function.

Thanks
Siva