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 (payslips) for a particular period. I can easily display a list of employees that do have transactions (payslips) for a particular period. I tried reversing this, but it doesn't seem to work, or I'm missing something somewhere. Please help. # Table structure for table employees emp_id emp_num emp_title emp_surname emp_name emp_initials emp_termdate // etc. INSERT INTO employees VALUES (1, 'EMP001', 'Mrs.', 'Surname1', 'Name1', 'N1.', '0000-00-00'); INSERT INTO employees VALUES (2, 'EMP002', 'Mr.', 'Surname2', 'Name2', 'N2.', '0000-00-00'); INSERT INTO employees VALUES (3, 'EMP003', 'Mr', 'Surname3', 'Name3', 'N3.', '0000-00-00'); INSERT INTO employees VALUES (4, 'EMP004', 'Mr.', 'Surname4', 'Name4', 'N4.', '2003-08-31'); INSERT INTO employees VALUES (5, 'EMP005', 'Mr.', 'Surname5', 'Name5', 'N5.', '2004-02-28'); INSERT INTO employees VALUES (6, 'EMP006', 'Mr.', 'Surname6', 'Name6', 'N6.', '0000-00-00'); INSERT INTO employees VALUES (7, 'EMP007', 'Mr.', 'Surname7', 'Name7', 'N7.', '0000-00-00'); # Table structure for table payperiods pp_id pp_period pp_status INSERT INTO payperiods VALUES (1, 'JAN 2004', 'inactive'); INSERT INTO payperiods VALUES (2, 'FEB 2004', 'active'); # Table structure for table transactions CREATE TABLE transactions ( tran_id int(11) NOT NULL auto_increment, pp_id int(11) NOT NULL default '0', emp_id int(11) NOT NULL default '0', tran_basicsal decimal(11,2) NOT NULL default '0.00', tran_OT_rate decimal(11,2) NOT NULL default '0.00', tran_OT_qty decimal(11,2) NOT NULL default '0.00', tran_DT_rate decimal(11,2) NOT NULL default '0.00', tran_DT_qty decimal(11,2) NOT NULL default '0.00', tran_bonus decimal(11,2) NOT NULL default '0.00', tran_commission decimal(11,2) NOT NULL default '0.00', tran_travelall decimal(11,2) NOT NULL default '0.00', tran_cellall decimal(11,2) NOT NULL default '0.00', tran_leavepdout_days decimal(11,2) NOT NULL default '0.00', tran_leavepdout_rate decimal(11,2) NOT NULL default '0.00', tran_uif_emp decimal(11,2) NOT NULL default '0.00', tran_uif_com decimal(11,2) NOT NULL default '0.00', tran_sdl decimal(11,2) NOT NULL default '0.00', tran_paye decimal(11,2) NOT NULL default '0.00', tran_staffloan decimal(11,2) NOT NULL default '0.00', tran_unpaidleave_days decimal(11,2) NOT NULL default '0.00', tran_unpaidleave_rate decimal(11,2) NOT NULL default '0.00', tran_leave_taken decimal(10,2) NOT NULL default '0.00', tran_sl_taken decimal(11,2) NOT NULL default '0.00', PRIMARY KEY (tran_id) ) TYPE=MyISAM PACK_KEYS=0 AUTO_INCREMENT=12 ; # # Dumping data for table transactions # INSERT INTO transactions VALUES (6, 1, 1, '3500.00', '29.84', '1.00', '39.78', '1.00', '40.00', '10.00', '20.00', '30.00', '0.00', '159.12', '36.70', '36.70', '36.70', '366.96', '50.00', '0.00', '159.12', '0.00', '0.00'); INSERT INTO transactions VALUES (7, 1, 2, '2000.00', '17.04', '1.00', '22.72', '1.00', '40.00', '10.00', '20.00', '30.00', '0.00', '90.88', '21.40', '21.40', '21.40', '213.98', '50.00', '0.00', '90.88', '0.00', '0.00'); INSERT INTO transactions VALUES (8, 1, 3, '9000.00', '68.18', '1.00', '90.90', '1.00', '40.00', '10.00', '20.00', '30.00', '0.00', '409.05', '92.59', '92.59', '92.59', '925.91', '50.00', '0.00', '409.05', '0.00', '0.00'); INSERT INTO transactions VALUES (11, 2, 1, '3500.00', '29.84', '1.00', '39.78', '1.00', '40.00', '10.00', '20.00', '30.00', '0.00', '159.12', '36.70', '36.70', '36.70', '366.96', '50.00', '0.00', '159.12', '0.00', '0.00'); INSERT INTO transactions VALUES (10, 2, 7, '2200.00', '16.67', '1.00', '22.22', '1.00', '40.00', '10.00', '20.00', '30.00', '0.00', '99.99', '23.39', '23.39', '23.39', '233.89', '50.00', '0.00', '99.99', '0.00', '0.00'); # -------------------------------------------------------- My query is as follows: <?php // IF COUNT OF EMPLOYEES DIFFER WITH COUNT OF TRANSACTIONS, DO THIS // DISPLAY ONLY EMPLOYEES THAT DON'T HAVE TRANSACTIONS FOR THE CURRENT ("active") PERIOD. else { $t1 = 'employees'; $t2 = 'transactions'; $selectempquery = mysql_query("SELECT DISTINCT $t1.*, $t2.emp_id FROM $t1 LEFT JOIN $t2 ON $t1.emp_id=$t2.emp_id WHERE NOT $t1.emp_termdate AND ($t2.pp_id != '$pp_id' OR $t2.pp_id IS NULL)"); // This doesn't work right // if i replace the above AND with: AND $t2.emp_id IS NULL"); // it won't return any rows if employees have transactions in other periods, // because it searches the ON $t1.emp_id = $t2.emp_id and doesn't // concider the period at all // Combining both these in the query just refuses to return any results. while ($row = @mysql_fetch_array($selectempquery)) { $variable3=$row['emp_num']; $variable4=$row['emp_title']; $variable5=$row['emp_initials']; $variable6=$row['emp_surname']; echo "<tr><td width=75 height=21>&nbsp;$variable3 </td><td width=225> <a href=".WEB_ROOT."procpayslip1.php?pp_id=$pp_id&emp_num=$variable3>$variable4 $variable5 $variable6</a></td></tr>"; } } ?> I concidered first selecting transactions that do exist in the period, but then I am not sure how to put this into an array in order to exclude it. A subquery doesn't work either and I'm using MySQL 4.0.24 will be upgrading soon to MySQL 4.1.11 The query substring looked like this: $t1 = 'employees'; $t2 = 'transactions'; $selectempquery = mysql_query("SELECT DISTINCT $t1.*, $t2.emp_id FROM $t1 LEFT JOIN $t2 ON $t2.emp_id = $t2.emp_id WHERE $t2.emp_id != (SELECT emp_id FROM transactions WHERE pp_id = '$pp_id')"); What is wrong here? It returns no rows and I would expect it to. Please help