1、需求
兩個表，投遞記錄表和封發開拆記錄表，現在想知道投遞日期距最後一次封發日期天數分布情況。
對這個需求，需要先查詢出投遞明細，同時要知道對應的郵件最後一次封發情況，如機構、日期等。
2、明細查詢
考慮到一天可能封發多次，所以取日期和時間都是最大的那條，語句如下：
select d.city,d.ssxs,d.zj_code,d.zj_mc,c.mail_num,
c.dlv_date,to_char(c.dlv_time,'hh24miss'), c.actual_goods_fee,
c.dlv_pseg_code,c.dlv_pseg_name,c.dlv_bureau_name,
c.dlv_staff_code,c.dlv_staff_name,c.signer_name,
a.deal_org_code,a.dlv_org_code,a.label_strip,a.deal_date,a.deal_time
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)
3、時限分布
有了明細語句，時間分布就比較簡單了，語句如下：
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
order by d.city, d.ssxs, d.zj_code
4、存在問題及解決
上面語句的查詢結果出來後，經核對，數字對不上，記錄變少了，差了很多，檢查發現有一部分郵件沒有分發記錄，不過這個數字很少，那麼原因出在哪兒呢？
原來原因出在最後乙個條件上，最後乙個條件是查出最大日期和最大時間，但是，最大日期的那條記錄時間不一定最大，結果導致，這些郵件都被涮下去了，為了得到正確結果，最後乙個條件改為：
and to_char(a.deal_date,'yyyymmdd')||to_char(a.deal_time,'000000') =
(select max(to_char(t.deal_date,'yyyymmdd')||to_char(t.deal_time,'000000'))
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)
時間按格式「000000」轉換是因為表中時間是時分秒組成的數值型字段，長度不定，按格式「000000」轉換後統一長度，便於比較大小
。比如日期時間合成結果：20140530 091239，就是2023年5月30日9時12分39秒。
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 to_char(a.deal_date,'yyyymmdd')||to_char(a.deal_time,'000000') =
(select max(to_char(t.deal_date,'yyyymmdd')||to_char(t.deal_time,'000000'))
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
order by d.city, d.ssxs, d.zj_code
to_char(t.deal_time+9000000)轉換結果：201405309091239
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