有表A大概三万多条数据，表B十二万多条数据，联合查询时速度超慢
select a.Country,a.City, count(b.*) as pvCount from a left join b on a.uid=b.uid where b.pcsDate>='"+tDate1+"' and b.pcsDate<='"+tDate2+"' group by a.Country,a.City order by pvCount descselect a.C
