oracle 数据同比遇到数据为0的情况怎么处理

最近需要做一个统计数据的报表，然后遇到了当数据为0的时候怎么进行数据同比
一直提示除数为0，我的sql粘贴如下，在线等答案~

select
a.*,
nvl(round(a.cr/lag(a.cr) over(partition by month order by a.stat_date)*100,2)-100,'0')||'%' hb
from (
select
t.stat_date,
substr(t.stat_date,0,4) year,
substr(t.stat_date,5,2) month,
t.wccb wccb,
t.tjtb tjtb,
t.cj cj,
trunc(t.cj/t.wccb,4) cr
from
(
select
substr(to_char(t.created_date,'yyyyMMdd'),0,6) stat_date,
count(t.th_id) WCCB,
sum(decode(t.apply_date,null,0,1)) TJTB,
sum(decode(t.elis_policy_no,null,0,1)) CJ
from life_th_app_policy_info t
group by substr(to_char(t.created_date,'yyyyMMdd'),0,6)
order by substr(to_char(t.created_date,'yyyyMMdd'),0,6)
) t
) a

a.cr/lag(a.cr)替换成decode(lag(a.cr),0,0,a.cr/lag(a.cr))
要判断为0的情况

select
ta.stat_date,
ta.wccb,
ta.tjtb,
ta.cj,
ta.cr,
decode(ta.tb,0,0,round((ta.cr-ta.tb)/ta.tb,4)) tb
from (
select
a.*,
lag(a.cr,1,0) over(partition by month order by a.stat_date) tb
from (
select
t.stat_date,
substr(t.stat_date,0,4) year,
substr(t.stat_date,5,2) month,
t.wccb wccb,
t.tjtb tjtb,
t.cj cj,
trunc(t.cj/t.wccb,4) cr
from
(
select
substr(to_char(t.created_date,'yyyyMMdd'),0,6) stat_date,
count(t.th_id) WCCB,
sum(decode(t.apply_date,null,0,1)) TJTB,
sum(decode(t.elis_policy_no,null,0,1)) CJ
from life_th_app_policy_info t
group by substr(to_char(t.created_date,'yyyyMMdd'),0,6)
order by substr(to_char(t.created_date,'yyyyMMdd'),0,6)
) t
) a order by a.stat_date
) ta