SELECT sum( IF( `tbl_payment_part`.`nominal_code` =2310, amount, NULL ) ) AS net_tax, sum( IF( `tbl_payment_part`.`nominal_code` >4000
AND `tbl_payment_part`.`nominal_code` <5000, amount, NULL ) ) AS net_amount, sum( IF( `tbl_payment_part`.`nominal_code` >1000
AND `tbl_payment_part`.`nominal_code` <2000, amount, NULL ) ) AS gross_amount,
`tbl_customer`.`F_NAME`
FROM `tbl_payment_part`, `tbl_invoice_payment` ,`tbl_invoice_cust`,`tbl_customer`,`tbl_invoice`
WHERE `tbl_payment_part`.`parent_payment_id`=`tbl_invoice_payment`.`id` AND `tbl_invoice_payment`.`invoice_number`=`tbl_invoice_cust`.`invoice_id`
AND `tbl_invoice_cust`.`customer_id`=`tbl_customer`.`id`  AND `tbl_invoice_payment`.`invoice_number`=`tbl_invoice`.`id`
AND `tbl_invoice`.`sales_rep`=1387
GROUP BY `tbl_customer`.`id`