數據序列

Question

我有如下表的順序編號：

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s^SQL的方式，如何創建下面的輸出？

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 

與上一行（按ID排序）相比，每次列obs中的值發生更改時，seq_num都會增加1。我可以很容易地在Excel中解決這個問題（使用簡單的公式），但無法在postgres中找出它。

Answer 1

，是這樣的：

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

您可以使用rownumber來做到這一點。

Answer 3

我已經想通了：使用分析功能

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