我有这个查询:SET@row_num=0;SELECT(SELECT@row_num:=@row_num+1)ASitempurchase_code,(SELECTsupplier_codeFROMqa_items_purchasesaWHEREa.item_invoicecodesupplier=b.item_invoicecodesupplierGROUPBYsupplier_codeORDERBYCOUNT(*)DESCLIMIT1)ASsupplier_code,(SELECTuser_codeFROMqa_items_purchasesaWHEREa.item_invoice