查询最大并发时间跨度数

Question

我有一个带有两个日期时间字段(CnxStartdatetime,CnxEnddatetime)的SQL Server表.每行代表信息的传输. 我试图找到基于这两个时间戳的最大并发传输数.我有一个工作查询,但它既缓慢又非常麻烦.我知道必须有一个更好的方法来解决这个问题,但不能提出任何问题.

对于当前版本,如果我以5"级别"运行并获得结果,我必须返回并添加大量SQL来测试是否存在6个并发传输的实例,等等.一旦查询获得7-8"级别"它变得非常慢.

当前版本的片段:

select 
    t1.id, t2.id, t3.id, t4.id, t5.id, t6.id, t7.id, t8.id, t9.id, t10.id

FROM
dbo.MyTable t1, dbo.MyTable t2, dbo.MyTable t3, dbo.MyTable t4, dbo.MyTable t5,
dbo.MyTable t6, dbo.MyTable t7, dbo.MyTable t8, dbo.MyTable t9, dbo.MyTable t10
WHERE
(((t2.cnxstartdatetime >= t1.cnxstartdatetime) and (t2.cnxstartdatetime <= t1.cnxenddatetime))
or ((t2.cnxenddatetime >= t1.cnxstartdatetime) and (t2.cnxenddatetime <= t1.cnxenddatetime)))
AND
t2.id != t1.id
AND
(((t3.cnxstartdatetime >= t2.cnxstartdatetime) and (t3.cnxstartdatetime >= t1.cnxstartdatetime)and (t3.cnxstartdatetime <= t1.cnxenddatetime) and (t3.cnxstartdatetime <= t2.cnxenddatetime))
or ((t3.cnxenddatetime >= t2.cnxstartdatetime) and (t3.cnxenddatetime >= t1.cnxstartdatetime)and (t3.cnxenddatetime <= t1.cnxenddatetime) and (t3.cnxenddatetime <= t2.cnxenddatetime)))
AND
t3.id != t2.id AND t3.id != t1.id
AND
(((t4.cnxstartdatetime >= t3.cnxstartdatetime) and (t4.cnxstartdatetime >= t1.cnxstartdatetime)and (t4.cnxstartdatetime >= t2.cnxstartdatetime) and (t4.cnxstartdatetime <= t1.cnxenddatetime) and (t4.cnxstartdatetime <= t3.cnxenddatetime)and (t4.cnxstartdatetime <= t2.cnxenddatetime))
or ((t4.cnxenddatetime >= t3.cnxstartdatetime) and (t4.cnxenddatetime >= t1.cnxstartdatetime)and (t4.cnxenddatetime >= t2.cnxstartdatetime) and (t4.cnxenddatetime <= t1.cnxenddatetime)and (t4.cnxenddatetime <= t3.cnxenddatetime)and (t4.cnxenddatetime <= t2.cnxenddatetime)))
AND
t4.id != t3.id AND t4.id != t2.id AND t4.id != t1.id
... *snip*

---

编辑许多回复建议我使用cross join.这并没有达到我想要的结果.这是cross join一个记录的"重叠" 结果的一个例子.这是它给我的ID列表中11787 你可以看到,11781并没有重叠,11774 这是一个简单,其时间跨度相交的任何记录列表11787

11774    2011-04-29 01:02:56.780    2011-04-29 01:02:58.793
11777    2011-04-29 01:02:56.780    2011-04-29 01:02:58.843
11778    2011-04-29 01:02:56.780    2011-04-29 01:02:58.950
11775    2011-04-29 01:02:56.793    2011-04-29 01:02:58.843
11776    2011-04-29 01:02:56.793    2011-04-29 01:02:58.890
11780    2011-04-29 01:02:58.310    2011-04-29 01:03:02.687
11779    2011-04-29 01:02:58.327    2011-04-29 01:03:02.543
11787    2011-04-29 01:02:58.530    2011-04-29 01:03:08.827 **
11781    2011-04-29 01:02:59.030    2011-04-29 01:03:05.187
11782    2011-04-29 01:02:59.247    2011-04-29 01:03:05.467
11784    2011-04-29 01:02:59.293    2011-04-29 01:03:05.810
11791    2011-04-29 01:03:00.107    2011-04-29 01:03:13.623
11786    2011-04-29 01:03:00.843    2011-04-29 01:03:08.983
11783    2011-04-29 01:03:02.560    2011-04-29 01:03:05.793
11785    2011-04-29 01:03:02.717    2011-04-29 01:03:07.357
11790    2011-04-29 01:03:05.200    2011-04-29 01:03:14.153
11804    2011-04-29 01:03:05.687    2011-04-29 01:03:25.577
11811    2011-04-29 01:03:07.093    2011-04-29 01:03:35.153
11799    2011-04-29 01:03:07.123    2011-04-29 01:03:24.437
11789    2011-04-29 01:03:08.793    2011-04-29 01:03:13.577

---

我也尝试用递归编写CTE,但我无法弄清楚如何确保当前与当前并发堆栈中的ID任何一个都不匹配ID.下面只是自我解决,直到达到极限.

WITH TransmissionConcurrency (StartTime, EndTime, ConcurrencyLevel) AS
(
    SELECT
        CnxStartDatetime AS StartTime,
        CnxEndDatetime AS EndTime,
        1 AS ConcurrencyLevel
    FROM dbo.MyTable

    UNION ALL

    SELECT
        CASE WHEN d.CnxStartDatetime > tc.StartTime THEN d.CnxStartDatetime ELSE tc.StartTime END AS StartTime,
        CASE WHEN d.CnxEndDatetime < tc.EndTime THEN d.CnxEndDatetime ELSE tc.EndTime END AS EndDate,
        tc.ConcurrencyLevel + 1 as ConcurrencyLevel
    FROM dbo.MyTable d
        INNER JOIN TransmissionConcurrency tc ON
            ((d.CnxStartDatetime between tc.StartTime and tc.EndTime)
            or
            (d.CnxEndDatetime between tc.StartTime and tc.EndTime)
            or
            (d.CnxStartDatetime <= tc.StartTime and d.CnxEndDatetime >= tc.EndTime))
)

SELECT * 
FROM TransmissionConcurrency
ORDER BY ConcurrencyLevel, StartTime, EndTime

---

我想出了下面的图表,试图更好地解释我在寻找什么.

A         [--------]
B    [-----]
C              [------]
D   [---]
E             [---]
F         [-]

在这个例子中,cross join方法会告诉我最大并发数A为6(Awith B, C, D, E and F)我正在寻找的最大并发数为3(A有B,F 或 A有C,E)

Answer 1

杰夫. 我曾经写过一个类似的查询 - 但在 Oracle 中 - 不确定这是否适用于 SQL-Server，但值得尝试：也许它会给你一些想法：

select
  t.time as b,
  lead(t.time)  over (order by t.time, t.weight desc) as e,
  sum(t.weight) over (order by t.time, t.weight desc) as cnt
from
  ( select trunc(:aStartWith)   as time,  0 as weight from dual
    union all
    select req_recieved as time, +1 as weight
      from log_tbl
      where trunc(req_recieved, 'mi') between :aStartWith - interval '10' minute and :aEndWith + interval '10' minute
    union all
    select response_sent as time, -1 as weight
      from log_tbl
      where trunc(req_recieved, 'mi') between :aStartWith - interval '10' minute and :aEndWith + interval '10' minute
    union all
    select trunc(:aEndWith) as time,  0 as weight from dual
  ) t

总体思路是，我遍历:aStartWith日期和:aEndWith日期之间的所有请求，为给定时间段内开始的每个请求分配 +1 权重部分，为同一时间段内结束的每个请求分配 -1 权重部分。

这里我假设请求不再是那10分钟（where trunc(req_recieved, 'mi') between :aStartWith - interval '10' minute and :aEndWith + interval '10' minute）；和select ... from dual是边界条件。

然后，通过分析函数，我找到请求的结束时间 ( ) 并对当前请求的权重求和 - 这将给出从时间 ( )开始到时间( ) 结束lead(t.time) over (order by t.time, t.weight desc) as e的多个请求。besum(t.weight) over (order by t.time, t.weight desc) as cnt

要找到最大请求数，您只需用所需的评估包装此查询即可。

您可以尝试一下这个场景是否适合您吗？希望如此:)