SQL：多表关联取最大日期的那条记录

作者：iamlasong

1、需求

两个表，投递记录表和封发开拆记录表，现在想知道投递日期距最后一次封发日期天数分布情况。

对这个需求，需要先查询出投递明细，同时要知道对应的邮件最后一次封发情况，如机构、日期等

2、明细查询

考虑到一天可能封发多次，所以取日期和时间都是最大的那条，语句如下：

select *
  from tb_evt_bag_mail_rela a,tb_evt_dlv c , tb_jg d
 where a.mail_num=c.mail_num
   and a.bag_actn_code = '3'
   and c.dlv_date between to_date('2014-6-1','yyyy-mm-dd') and to_date('2014-6-1','yyyy-mm-dd')
   and c.dlv_bureau_org_code = d.zj_code
   and c.dlv_sts_code = 'I'
   and (a.deal_date,a.deal_time)=(select max(t.deal_date),max(t.deal_time) from tb_evt_bag_mail_rela t
        where t.mail_num = a.mail_num
          and t.bag_actn_code = '3'
     group by t.mail_num, t.bag_actn_code)

有了明细语句，时间分布就比较简单了，语句如下：

select d.city, d.ssxs,d.zj_code,d.zj_mc, count(*) ttzl,
       Sum(Decode(c.Dlv_Date - a.deal_date, 0, 1, 0)) t0,
       Sum(Decode(c.Dlv_Date - a.deal_date, 1, 1, 0)) t1,
       Sum(Decode(c.Dlv_Date - a.deal_date, 2, 1, 0)) t2,
       Sum(Decode(c.Dlv_Date - a.deal_date, 3, 1, 0)) t3,
       Sum(Decode(c.Dlv_Date - a.deal_date, 4, 1, 0)) t4,
       Sum(Decode(c.Dlv_Date - a.deal_date, 5, 1, 0)) t5
  from tb_evt_bag_mail_rela a,tb_evt_dlv c , tb_jg d
 where a.mail_num=c.mail_num
   and a.bag_actn_code = '3'
   and c.dlv_date between to_date('2014-6-1','yyyy-mm-dd') and to_date('2014-6-1','yyyy-mm-dd')
   and c.dlv_bureau_org_code = d.zj_code
   and c.dlv_sts_code = 'I'
   --and d.jgfl='yz'
   and (a.deal_date,a.deal_time)=(select max(t.deal_date),max(t.deal_time) from tb_evt_bag_mail_rela t
        where t.mail_num = a.mail_num
          and t.bag_actn_code = '3'
     group by t.mail_num, t.bag_actn_code)
 group by d.city, d.ssxs,d.zj_code,d.zj_mc