[PHP-DB] MySQL query + PHP : Warning: implode() [function.implode]: Bad arguments : What's wrong here?

I have 2 tables employees transactions. 'employees' carry info about the employees and transactions carry there payslip info for each period. I am trying to display a list of employees that don't have transactions in the current ($pp_id) period, thus doing an array of the $emp_ids, having

[PHP-DB] MySQL JOIN query : Seeking solution - Please Help

I am still new to this, but I turned the manual upside down, or at least I tried. I am designing a payroll application by which payslips can be processed for each employee for each period. The problem lays where I would like to display a list of employees that don't have transactions