我用的是postgresql，sql中有个province条件，我把province的值更换后，出现了某个值为条件时可以执行成功（速度较快），然后province为其他值时执行失败（长时间执行不出结果），这可能是什么原因？

with first_condition as ( 
                    select  monitor_point, monitor_info, company, count(distinct(month)) as continuous_month  
                    from craw_day_merge where day>='2020-02-01' and day<= '2020-03-31'   and valid_complete < 0.75  and province='安徽'  
                    group by company, monitor_point, monitor_info having sum(exceed_count)=0 
                    and count(distinct(month)) >= '1'           
              )
            select merge.company, 
            merge.monitor_point, merge.monitor_info, merge.province, first_condition.continuous_month
             from craw_day_merge merge inner join first_condition  
            on merge.day>='2019-02-01' and merge.day<= '2020-03-31' and 
            merge.monitor_point=first_condition.monitor_point and merge.monitor_info=first_condition.monitor_info and 
            merge.company=first_condition.company 
            group by  merge.company, 
            merge.monitor_point, merge.monitor_info, merge.province, first_condition.continuous_month;

explain + sql可以看到执行过程，注意fliter，recheck index，lossy这些会导致慢查询的因素，换sql写法或者加索引去解决。
如果执行过程没有问题，可以尝试reindex索引或者vaccum这个表。