I do have the following table:
create table test_seq (id int, obs int);
insert into test_seq values (1,1);
insert into test_seq values (2,1);
insert into test_seq values (3,1);
insert into test_seq values (4,0);
insert into test_seq values (5,0);
insert into test_seq values (6,1);
insert into test_seq values (7,1);
insert into test_seq values (8,0);
insert into test_seq values (9,0);
insert into test_seq values (10,1);
insert into test_seq values (11,0);
Is there s SQL way, how to create the following output?
id obs seq_num
1 1 1
2 1 1
3 1 1
4 0 2
5 0 2
6 1 3
7 1 3
8 0 4
9 0 4
10 1 5
11 0 6
seq_num is increased by 1 every time when value in column obs is changed compared to the previous row (ordered by id). I can solve this easily in Excel (using simple if formula), but can't figure out this in postgres.
using analytic functions, something like :
select id, obs, sum(cnt) over (order by id) as seq_num
from (
select id, obs, case when obs <> (lag(obs) over (order by id)) then 1 else 0 end as cnt
from test_seq
)
order by id;
I've figured it out:
with t as (
select
id,
obs,
case when lag(obs,1) over (order by id) <> obs then 1 else 0 end as test
from
tmp.test_seq
)
select
*,
sum(test) over (order by id rows between unbounded preceding and current row) + 1
from
t
你可以使用rownumber来做到这一点。
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