數據序列的順序編號

Question

我有下表：

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);

有SQL方法，如何創建以下輸出？

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

每當列obs中的值與前一行（按id排序）相比更改時，seq_num增加1。 我可以在Excel中輕松解決這個問題（使用簡單的if公式），但在postgres中無法弄清楚這一點。

Answer 1

使用分析函數，如：

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;

Answer 2

我弄清楚了：

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

Answer 3

你可以使用rownumber來做到這一點。