postgres 我得到了一组数字，例如"1,2,3,6,7,8,11,12,15,18,19,20"获得每组连续数字的最大值

Question

连续数字按以下查询分组，但我不知道如何获得每组连续数字的最大值

with trans as (
select c1, 
case when lag(c1) over (order by c1) = c1 - 1 then 0 else 1 end as new
from table1
), groups as (
select c1, sum(new) over (order by c1) as grpnum
from trans
), ranges as (
select grpnum, min(c1) as low, max(c1) as high
from groups
group by grpnum
), texts as (
select grpnum, 
case 
when low = high then low::text 
else low::text||'-'||high::text
end as txt
from ranges
)
select string_agg(txt, ',' order by grpnum) as number
from texts;

Answer 1

在R中，我们可以创建一个包含diff和cumsum的群，然后用tapply得到每个群的向量的max

grp <- cumsum(c(TRUE, diff(v1) > 1))
tapply(v1, grp, FUN = max)
#   1  2  3  4  5 
#   3  8 12 15 20 

数据

v1 <- c(1, 2, 3, 6, 7, 8, 11, 12, 15, 18, 19, 20)