agipamp's questions

如果我的 Redshift/Postgresql 中有一个名为：conn_log 的简单表

从性能来看，这两个命令有什么区别？

select t1.wifi_name, (t2.sconn*100)::numeric/t1.ttconn
from (select wifi_name, count(*) as ttconn 
      from conn_log 
      group by wifi_name) t1, 
     (select wifi_name, count(*) as sconn 
      from conn_log 
      where success = 1 
      group by wifi_name) t2
where t1.wifi_name = t2.wifi_name;

第二个查询：

select t1.wifi_name, (t2.sconn*100)::numeric/t1.ttconn
from (select wifi_name, count(*) as ttconn 
      from conn_log 
      group by wifi_name) t1
join
     (select wifi_name, count(*) as sconn 
      from conn_log 
      where success = 1 
      group by wifi_name) t2
on t1.wifi_name = t2.wifi_name