纵向求最大最小与横向求最大最小greatest(),least(),max(),min()

greatest (a,b,c,d,e)
greatest 求的是某几列的最大值，横向求最大(一行的多列记录求最大)

注意:a,b,c,d,e列中不能出现null值，否则greatest()返回值为null值

select
greatest(
nvl(substr(a.update_time,1,10),0),nvl(substr(b.dt_editdate,1,10),0),nvl(substr(coalesce(c.editdate,c.adddate),1,10),0)
,nvl(substr(e.update_time,1,10),0),nvl(substr(f.update_time,1,10),0),nvl(substr(g.update_time,1,10),0)) update_time
from statistics.corp_basic_info_ods a
left join usercenter.ucenter_company_ods b on a.tax_num = b.c_taxnum
left join orderdb.orders_ods c on a.tax_num = c.buyer_taxnum
left join statistics.corp_deliver_config_info_ods e on a.tax_num = e.tax_num
left join statistics.corp_equip_invoice_ods f on a. tax_num = f.taxnum
left join statistics.corp_equip_invoice_sub_client_ods g on f.id = g.invoice_equipment_id

least(a,b,c,d,e)
求多列中的最小值，横向求最小

注意:a,b,c,d,e列中不能出现null值，否则greatest()返回值为null值

max(a)
求a列中的最大值
纵向求最大(一列的多行记录求最大)

min(a)
求a列中的最小值
纵向求最小(一列的多行记录求最小)