SQL:为什么在一条语句中计算两个表的计数很慢?

因为您正在交叉连接那些表,在那里使用旧式连接。我猜你不知道会发生这种事, but you can read here on why you shouldn't use them

我想你想要的是一张桌子上的结果。如果是,请使用子查询。

select (
    select count(distinct ec.logicalid) 
    from event_counts ec 
    where ec.eventname = 'Searches'
   ) as firstcount, 
       (
    select count(a.logicalid) 
    from sf_accounts a
   ) as secondcount

否则,请正确联接表

select 
   count(distinct ec.logicalid) 
   ,count(a.logicalid)
from event_counts ec
inner join sf_accounts a on a.logicalid = ec.logicalid
where ec.eventname = 'Searches'