表结构
日期 date
用户 userid
其他字段
需求：查询把date分组，查出date之前从未出现过的userid个数，即新增用户数
如：
date userid 其他字段
2012-10-01 1
2012-10-01 2
2012-10-01 3
2012-09-22 1
2012-08-22 1
结果为2、3，即一共2个，date、userid皆有索引，查询效率要高，因为数据量很大
------解决方案--------------------
- SQL code
--为什么需要对日期进行分组呢，你不是统计指定日期前未出现过的人数吗？with t("date",userid) as(select to_date('2012-10-01','yyyy-mm-dd'),1 from dualunion all select to_date('2012-10-01','yyyy-mm-dd'),2 from dualunion all select to_date('2012-10-01','yyyy-mm-dd'),3 from dualunion all select to_date('2012-09-22','yyyy-mm-dd'),1 from dualunion all select to_date('2012-08-22','yyyy-mm-dd'),1 from dual)select count(distinct userid) total from t where t."date">trunc(sysdate) and not exists(select 1 from t t1 where t.userid=t1.userid and t1."date"<=trunc(sysdate));
------解决方案--------------------
select Count(*) from tb where date>to_date(date,'yyyy-mm-dd') and userid not in
(select distinct userid from tb where date<=to_date(date,'yyyy-mm-dd'))
------解决方案--------------------
还有你的userid,date最好有联合索引，执行效率应会高些
------解决方案--------------------
- SQL code
with t (dt, userid) as (select to_date('2012-10-01', 'yyyy-mm-dd'), 1 from dualunion all select to_date('2012-10-01', 'yyyy-mm-dd'), 2 from dualunion all select to_date('2012-10-01', 'yyyy-mm-dd'), 3 from dualunion all select to_date('2012-09-22', 'yyyy-mm-dd'), 1 from dualunion all select to_date('2012-08-22', 'yyyy-mm-dd'), 1 from dual)select distinct(userid) from t where not exists(select 1 from t t1 where t.userid=t1.userid and t1.dt < to_date('2012-09-30','yyyy-mm-dd'));