我有这个问题，因为我刚刚发现这个网站，我决定把它发布在这里。让我们说，我有一个表的时间戳和一个给定的“对象”（通用含义，而不是OOP对象）的状态;有没有一种最佳的方式来计算一个状态和另一个（或相同）状态（我称之为“旅行”）的下一次出现之间的时间与单个SQL语句（内部SELECTs和UNION不计算在内）之间的时间？例如：对于以下情况，初始和完成之间的行程时间为6天，但在初始和复审之间为2天。关系数据库中的旅行时间计算？
2008-08-01 13:30:00 - 初始
2008-08-02 13:30:00 - 工作
2008-08-03 13:30:00 - 回顾
2008- 08-04 13:30:00 - 工作
2008-08-05 13:30:00 - 评论
2008-08-06 13:30:00 - 接受
2008-08-07 13:30:00 - 完成
不需要是通用的，只是说什么SGBD你的s如果不是通用的，解决方案是特定的。
我不认为你可以用一条SQL语句得到答案，因为你试图从许多记录中获得一个结果。在SQL中实现这一点的唯一方法是获取两个不同记录的时间戳字段并计算差异（datediff）。因此，需要联合或内联合。
我不确定我是否完全理解这个问题，但是您可以执行类似于以下内容的操作，即一次读取表格，然后使用派生表格来计算它。 SQL Server代码：
CREATE TABLE #testing
(
eventdatetime datetime NOT NULL,
state varchar(10) NOT NULL
)
INSERT INTO #testing (
eventdatetime,
state
)
SELECT '20080801 13:30:00', 'Initial' UNION ALL
SELECT '20080802 13:30:00', 'Work' UNION ALL
SELECT '20080803 13:30:00', 'Review' UNION ALL
SELECT '20080804 13:30:00', 'Work' UNION ALL
SELECT '20080805 13:30:00', 'Review' UNION ALL
SELECT '20080806 13:30:00', 'Accepted' UNION ALL
SELECT '20080807 13:30:00', 'Done'
SELECT DATEDIFF(dd, Initial, Review)
FROM (
SELECT MIN(CASE WHEN state='Initial' THEN eventdatetime END) AS Initial,
MIN(CASE WHEN state='Review' THEN eventdatetime END) AS Review
FROM #testing
) AS A
DROP TABLE #testing
create table A (
At datetime not null,
State varchar(20) not null
)
go
insert into A(At,State)
select '2008-08-01T13:30:00','Initial' union all
select '2008-08-02T13:30:00','Work' union all
select '2008-08-03T13:30:00','Review' union all
select '2008-08-04T13:30:00','Work' union all
select '2008-08-05T13:30:00','Review' union all
select '2008-08-06T13:30:00','Accepted' union all
select '2008-08-07T13:30:00','Done'
go
--Find trip time from Initial to Done
select DATEDIFF(day,t1.At,t2.At)
from
A t1
inner join
A t2
on
t1.State = 'Initial' and
t2.State = 'Review' and
t1.At < t2.At
left join
A t3
on
t3.State = 'Initial' and
t3.At > t1.At and
t4.At < t2.At
left join
A t4
on
t4.State = 'Review' and
t4.At < t2.At and
t4.At > t1.At
where
t3.At is null and
t4.At is null
没有说是否加入被允许。加入到t3和t4（以及它们的比较）可以让你说出是否需要最早或最新的开始和结束状态（在这种情况下，我要求最新的“初始”和最早的“评论”）
在真正的代码，我开始和结束的状态将参数
编辑：哎呀，需要包括“t3.At < t2.At”和“t4.At> t1.At”，要解决的一些奇怪的序列（例如，如果我们删除了第二个“审阅”，然后从“工作”查询到“审阅”，则原始查询将失败）
如果您有序列号以及时间戳：在大多数RDBMS中，您可以创建一个自动增量列d不会更改任何INSERT语句。然后你加入表其自身的副本来获得增量
select after.moment - before.moment, before.state, after.state
from object_states before, object_states after
where after.sequence + 1 = before.sequence
（其中SQL语法的细节将根据该数据库系统而异）。
-- Oracle SQl
CREATE TABLE ObjectState
(
startdate date NOT NULL,
state varchar2(10) NOT NULL
);
insert into ObjectState
select to_date('01-Aug-2008 13:30:00','dd-Mon-rrrr hh24:mi:ss'),'Initial' union all
select to_date('02-Aug-2008 13:30:00','dd-Mon-rrrr hh24:mi:ss'),'Work' union all
select to_date('03-Aug-2008 13:30:00','dd-Mon-rrrr hh24:mi:ss'),'Review' union all
select to_date('04-Aug-2008 13:30:00','dd-Mon-rrrr hh24:mi:ss'),'Work' union all
select to_date('05-Aug-2008 13:30:00','dd-Mon-rrrr hh24:mi:ss'),'Review' union all
select to_date('06-Aug-2008 13:30:00','dd-Mon-rrrr hh24:mi:ss'),'Accepted' union all
select to_date('07-Aug-2008 13:30:00','dd-Mon-rrrr hh24:mi:ss'),'Done';
-- Days in between two states
select o2.startdate - o1.startdate as days
from ObjectState o1, ObjectState o2
where o1.state = 'Initial'
and o2.state = 'Review';
我认为你的步骤（您的行程中的每个记录可以被看作是一个步骤）可以被地方组合在一起作为同一活动的一部分。然后，可以将你的信息就可以了数据，例如：
SELECT Min(Tbl_Step.dateTimeStep) as tripBegin, _
Max(Tbl_Step.dateTimeStep) as tripEnd _
FROM
Tbl_Step
WHERE
id_Activity = 'AAAAAAA'
利用这个原理，你就可以计算出样的活动等的步数等聚集。但是你不会找到一种SQL方法来计算两步之间的差距这样的值，因为这样的数据不属于第一步或第2步。一些报告工具使用他们所称的“运行总和”来计算这些中间数据。根据您的目标，这可能是您的解决方案。
以下是使用分析函数的Oracle方法。
with data as (
SELECT 1 trip_id, to_date('20080801 13:30:00','YYYYMMDD HH24:mi:ss') dt, 'Initial' step from dual UNION ALL
SELECT 1 trip_id, to_date('20080802 13:30:00','YYYYMMDD HH24:mi:ss') dt, 'Work' step from dual UNION ALL
SELECT 1 trip_id, to_date('20080803 13:30:00','YYYYMMDD HH24:mi:ss') dt, 'Review' step from dual UNION ALL
SELECT 1 trip_id, to_date('20080804 13:30:00','YYYYMMDD HH24:mi:ss') dt, 'Work' step from dual UNION ALL
SELECT 1 trip_id, to_date('20080805 13:30:00','YYYYMMDD HH24:mi:ss') dt, 'Review' step from dual UNION ALL
SELECT 1 trip_id, to_date('20080806 13:30:00','YYYYMMDD HH24:mi:ss') dt, 'Accepted' step from dual UNION ALL
SELECT 1 trip_id, to_date('20080807 13:30:00','YYYYMMDD HH24:mi:ss') dt, 'Done' step from dual)
select trip_id,
step,
dt - lag(dt) over (partition by trip_id order by dt) trip_time
from data
/
1 Initial
1 Work 1
1 Review 1
1 Work 1
1 Review 1
1 Accepted 1
1 Done 1
这些在传统上我们可能使用自连接的情况下非常常用。
PostgreSQL的语法：
DROP TABLE ObjectState;
CREATE TABLE ObjectState (
object_id integer not null,--foreign key
event_time timestamp NOT NULL,
state varchar(10) NOT NULL,
--Other fields
CONSTRAINT pk_ObjectState PRIMARY KEY (object_id,event_time)
);
对于给定的状态，查找第一个如下因素给定类型的状态
select parent.object_id,parent.event_time,parent.state,min(child.event_time) as ch_event_time,min(child.event_time)-parent.event_time as step_time
from
ObjectState parent
join ObjectState child on (parent.object_id=child.object_id and parent.event_time<child.event_time)
where
--Starting state
parent.object_id=1 and parent.event_time=to_timestamp('01-Aug-2008 13:30:00','dd-Mon-yyyy hh24:mi:ss')
--needed state
and child.state='Review'
group by parent.object_id,parent.event_time,parent.state;
此查询不是最短的更多钞票，但它应该是很容易理解和使用部分其他查询：
列出事件及其持续时间给定o bject
select parent.object_id,parent.event_time,parent.state,min(child.event_time) as ch_event_time,
CASE WHEN parent.state<>'Done' and min(child.event_time) is null THEN (select localtimestamp)-parent.event_time ELSE min(child.event_time)-parent.event_time END as step_time
from
ObjectState parent
left outer join ObjectState child on (parent.object_id=child.object_id and parent.event_time<child.event_time)
where parent.object_id=4
group by parent.object_id,parent.event_time,parent.state
order by parent.object_id,parent.event_time,parent.state;
列表当前状态为未 “完成”
select states.object_id,states.event_time,states.state,(select localtimestamp)-states.event_time as step_time
from
(select parent.object_id,parent.event_time,parent.state,min(child.event_time) as ch_event_time,min(child.event_time)-parent.event_time as step_time
from
ObjectState parent
left outer join ObjectState child on (parent.object_id=child.object_id and parent.event_time<child.event_time)
group by parent.object_id,parent.event_time,parent.state) states
where
states.object_id not in (select object_id from ObjectState where state='Done')
and ch_event_time is null;
测试数据
insert into ObjectState (object_id,event_time,state)
select 1,to_timestamp('01-Aug-2008 13:30:00','dd-Mon-yyyy hh24:mi:ss'),'Initial' union all
select 1,to_timestamp('02-Aug-2008 13:40:00','dd-Mon-yyyy hh24:mi:ss'),'Work' union all
select 1,to_timestamp('03-Aug-2008 13:50:00','dd-Mon-yyyy hh24:mi:ss'),'Review' union all
select 1,to_timestamp('04-Aug-2008 14:30:00','dd-Mon-yyyy hh24:mi:ss'),'Work' union all
select 1,to_timestamp('04-Aug-2008 16:20:00','dd-Mon-yyyy hh24:mi:ss'),'Review' union all
select 1,to_timestamp('06-Aug-2008 18:00:00','dd-Mon-yyyy hh24:mi:ss'),'Accepted' union all
select 1,to_timestamp('07-Aug-2008 21:30:00','dd-Mon-yyyy hh24:mi:ss'),'Done';
insert into ObjectState (object_id,event_time,state)
select 2,to_timestamp('01-Aug-2008 13:30:00','dd-Mon-yyyy hh24:mi:ss'),'Initial' union all
select 2,to_timestamp('02-Aug-2008 13:40:00','dd-Mon-yyyy hh24:mi:ss'),'Work' union all
select 2,to_timestamp('07-Aug-2008 13:50:00','dd-Mon-yyyy hh24:mi:ss'),'Review' union all
select 2,to_timestamp('14-Aug-2008 14:30:00','dd-Mon-yyyy hh24:mi:ss'),'Work' union all
select 2,to_timestamp('15-Aug-2008 16:20:00','dd-Mon-yyyy hh24:mi:ss'),'Review' union all
select 2,to_timestamp('16-Aug-2008 18:02:00','dd-Mon-yyyy hh24:mi:ss'),'Accepted' union all
select 2,to_timestamp('17-Aug-2008 22:10:00','dd-Mon-yyyy hh24:mi:ss'),'Done';
insert into ObjectState (object_id,event_time,state)
select 3,to_timestamp('12-Sep-2008 13:30:00','dd-Mon-yyyy hh24:mi:ss'),'Initial' union all
select 3,to_timestamp('13-Sep-2008 13:40:00','dd-Mon-yyyy hh24:mi:ss'),'Work' union all
select 3,to_timestamp('14-Sep-2008 13:50:00','dd-Mon-yyyy hh24:mi:ss'),'Review' union all
select 3,to_timestamp('15-Sep-2008 14:30:00','dd-Mon-yyyy hh24:mi:ss'),'Work' union all
select 3,to_timestamp('16-Sep-2008 16:20:00','dd-Mon-yyyy hh24:mi:ss'),'Review';
insert into ObjectState (object_id,event_time,state)
select 4,to_timestamp('21-Aug-2008 03:10:00','dd-Mon-yyyy hh24:mi:ss'),'Initial' union all
select 4,to_timestamp('22-Aug-2008 03:40:00','dd-Mon-yyyy hh24:mi:ss'),'Work' union all
select 4,to_timestamp('23-Aug-2008 03:20:00','dd-Mon-yyyy hh24:mi:ss'),'Review' union all
select 4,to_timestamp('24-Aug-2008 04:30:00','dd-Mon-yyyy hh24:mi:ss'),'Work';
我试图做到这一点在MySQL的对象。您将需要使用一个变量，因为在MySQL的无等级的功能，所以它会是这样的：
set @trip1 = 0; set @trip2 = 0;
SELECT trip1.`date` as startdate, datediff(trip2.`date`, trip1.`date`) length_of_trip
FROM
(SELECT @trip1 := @trip1 + 1 as rank1, `date` from trip where state='Initial') as trip1
INNER JOIN
(SELECT @trip2 := @trip2 + 1 as rank2, `date` from trip where state='Done') as trip2
ON rank1 = rank2;
我假设你要计算“初始”和“完成”状态之间的时间。
+---------------------+----------------+
| startdate | length_of_trip |
+---------------------+----------------+
| 2008-08-01 13:30:00 | 6 |
+---------------------+----------------+
好吧，这是一个有点超出有点怪，但是我建了一个Web应用程序来跟踪我妻子的收缩，我们生了一个孩子之前，这样我可以从作品看，当它越来越接近时间去医院。无论如何，我很容易以两种观点来构建这个基本的东西。
create table contractions time_date timestamp primary key;
create view contraction_time as
SELECT a.time_date, max(b.prev_time) AS prev_time
FROM contractions a, (SELECT contractions.time_date AS prev_time
FROM contractions) b
WHERE b.prev_time < a.time_date
GROUP BY a.time_date;
create view time_between as
SELECT contraction_time.time_date, contraction_time.prev_time, contraction_time.time_date - contraction_time.prev_time
FROM contraction_time;
这可以作为一个子查询来实现明显为好，但我用其他的东西中间的意见为好，所以这个结果不错。