sql语句:
create table dispatch_result ( dr_id number not null, sheet_id number, check_next varchar(20), check_time date, check_sn char(8), check_comment varchar(255), check_status number, constraint PK_RESULT primary key (dr_id) );
DR_ID SHEET_ID CHECK_NEXT CHECK_TIME CHECK_SN CHECK_COMMENT CHECK_STATUS
---------- ---------- -------------------- ----------- -------- -------------------------------------------------------------------------------- ------------
1 1 10001 2012/8/12 11:11:23 10000 1
2 1 10002 2012/9/15 11:15:24 10001 2
3 2 10001 2012/8/15 9:16:10 10000 1
4 2 10002 2012/9/18 11:16:23 10001 2
查询以SHEET_ID 分组取最大时间记录:
第一种子查询方式:
select * from dispatch_result dr where dr.check_time=( select max(check_time) from dispatch_result where sheet_id=dr.sheet_id)
第二种group by方式:
select t1.* from dispatch_result t1 right join (select sheet_id,max(check_time) ct from dispatch_result group by sheet_id) t2 on t2.sheet_id=t1.sheet_id and t2.ct=t1.check_time
或
select * from dispatch_result inner join (select max(dr.check_time) as check_time, dr.sheet_id from dispatch_result dr group by dr.sheet_id) t1 using(check_time,sheet_id);
再或者
select t1.* from dispatch_result t1 WHERE (t1.sheet_id,t1.check_time) IN (select sheet_id,max(check_time) ct from dispatch_result group by sheet_id)
第三种partition by方式:
select t2.* from (select t1.*,row_number() over (partition by t1.sheet_id order by t1.check_time desc nulls last) rn from dispatch_result t1) t2 where rn=1
结果都是一样的,至于效率求大神指教。