读者 自己加一个字段 借阅册数
update a
set 借阅册数 = ( select count(1) from 借阅 where 读者编号 = a.编号 and datecol between '时间1' and '时间2')
from 读者 a
update a
set 借阅册数 = ( select count(1) from 借阅 where 读者编号 = a.编号 and datecol between '时间1' and '时间2')
from 读者 a
set 借阅册数 = (select count(*) from 借阅 where 编号 = 读者.编号 and year(日期) between 2003 and 2006)
update 读者
set 借阅册数 = (select count(*) from 借阅 where 编号 = 读者.编号 and year(日期) between 2003 and 2006)
from 读者
然后再update 。