SELECT bill_invoice_data_8.cid,bill_invoice_data_8.summ,contract_balance.summa3 FROM bill_invoice_data_8 LEFT JOIN contract_balance ON bill_invoice_data_8.cid=contract_balance.cid AND bill_invoice_data_8.mm=contract_balance.mm-1 AND bill_invoice_data_8.yy=contract_balance.yy AND bill_invoice_data_8.create_dt = '2011-05-31' WHERE contract_balance.mm=5;

SELECT c.title, cb.summa3, bid.summ FROM contract_balance cb LEFT JOIN bill_invoice_data_8 bid ON cb.cid=bid.cid AND bid.yy=2011 AND bid.mm=5 LEFT JOIN contract c ON cb.cid=c.id WHERE cb.yy=2011 AND cb.mm=5 AND cb.summa3>0 HAVING bid.summ IS NULL;

SELECT c.title, cb.summa3, bid.summ FROM contract_balance cb LEFT JOIN bill_invoice_data_8 bid ON cb.cid=bid.cid AND bid.yy=2011 AND bid.mm=4 LEFT JOIN contract c ON cb.cid=c.id WHERE cb.yy=2011 AND cb.mm=5 AND cb.summa3>0 AND fc=1;