检查值是 SQL 中的第二天还是前一天

Question

I'm trying to count how many times the next or previous day of a day has a certain value when that day has a certain value. (I simplify the database structures to make you understand better what I need) Example:

Date          Event
2015-01-01       x
2015-01-02       x
2015-01-03      rest
2015-01-04      sick
2015-01-05       x
2015-01-06      sick
2015-01-07      rest
2015-01-08       x
2015-01-09       x

I need to count how many days a person is sick after or before the rest day. In this case the result from the query should be: 2

Answer 1

You can use a cumulative sum of 'rest' to get groups. Then aggregate and filter:

select count(*)
from (select t.*,
             sum(case when event = 'rest' then 1 else 0 end) over (order by date) as rest_grp
      from t
     ) t
where state = 'sick' 
group by rest_grp;

This actually returns three rows -- because there are three gruops (before the rest, in-between, and after the last).

If you specifically want the middle group, then use:

where state = 'sick' and rest_grp = 1