计算SQL Server中布尔值更改的次数

Question

我有这张桌子:

     [SDate - DateTime]                 [Value] - Represents a boolean
    2010-11-16 10:10:00                    1
    2010-11-16 10:11:00                    0
    2010-11-16 10:12:00                    1
    2010-11-16 10:13:00                    1

我需要一个查询来计算值变化的次数.

例如:

    2010-11-16 10:10:00                    0
    2010-11-16 10:11:00                    1
    2010-11-16 10:12:00                    0
    2010-11-16 10:13:00                    0
    2010-11-16 10:14:00                    1
    2010-11-16 10:15:00                    0
    2010-11-16 10:16:00                    1
    ...
                                       5 changes

---

    2010-11-16 10:10:00                    0
    2010-11-16 10:11:00                    0
    2010-11-16 10:12:00                    0
    2010-11-16 10:13:00                    1
    2010-11-16 10:14:00                    1
    2010-11-16 10:15:00                    1
    2010-11-16 10:16:00                    1
    ...                                       
                                        1 change

Answer 1

你可以这样做lag():

select count(*)
from (select t.*, lag(value) order by (sdate) as prev_value
      from table t
     ) t
where prev_value <> value ;