直到某个时间点的列的SQL平均值

select id, date, time,
       avg(time) over (partition by id order by date) as avg_time,
       row_number() over (partition by id order by date) as n_loans
from t;

也许,由于您没有提到dbms,我尝试了几乎所有dbms的方法,比如via join

    Select * from ( 
      ( Select id,date,count(*)
        from table group by id,date) t1 
           JOIN
        (SELECT AVG(TIME)
          FROM TABLE
         GROUP BY ID  ) t2
          ON 
        t1.ID =t2.id )