Question

我试图找到一种方法来实现这一目标而不使用游标。

我有一组总共约1300万条记录的数据。一条记录与下一条记录之间的间隔会有所不同，但都在5到20分钟之间。我需要创建一个新的数据表，但选择数据，这样一条记录与下一条记录之间至少有30分钟的差距。

例如，如果我有这个：

VID | Datetime
1   |  2016-01-01 00:00
1   |  2016-01-01 00:10
1   |  2016-01-01 00:12
1   |  2016-01-01 00:25
2   |  2016-01-01 00:40
4   |  2016-01-01 01:00
4   |  2016-01-01 02:13
6   |  2016-01-01 02:23
7   |  2016-01-01 02:25
8   |  2016-01-01 02:49
9   |  2016-01-01 02:59
9   |  2016-01-01 03:01
9   |  2016-01-01 03:09
9   |  2016-01-01 03:24
9   |  2016-01-01 04:05

新表格如下所示：

VID | Datetime
1   |  2016-01-01 00:00
2   |  2016-01-01 00:40
4   |  2016-01-01 02:13
8   |  2016-01-01 02:49
9   |  2016-01-01 03:24

我可以用光标做到这一点，但对于数以百万计的疯狂记录。我已经看到过类似情况下提到的一种奇怪的更新，但我不确定那是什么。

目前正在使用SQL Server 2014.非常感谢任何帮助。

Answer 1

如果你有一个标识符列而不是[vid]，事情会容易得多。如果是这种情况，那么你可以这样做：

with mycte (id, mydate, keepthis, offset)
as
(
    select
        id,
        mydate,
        1 keepthis,
        0 offset
    from mytable where id = 1
    union all
    select
        t.id,
        t.mydate,
        case when datediff(mi, o.mydate, t.mydate)+o.offset >= 30 then 1 else 0 end keepthis,
        case when datediff(mi, o.mydate, t.mydate)+o.offset >= 30 then 0 else datediff(mi, o.mydate, t.mydate)+o.offset end
    from mytable t join mycte o on t.id = o.id+1
)

select id,mydate from mycte where keepthis=1

Answer 2

在盒子外思考一下，如果允许在每30分钟的间隔内获得最早的行，那么我有一个有效的解决方案。

注意事项：

此时我假设您的数据可能会追溯到30年前。 1300万个间隔接近计数表配置方式的极限，因此如果超过16密耳，则需要进行更改
您可能需要将CTE分解为临时表并添加索引以获得对该数据的良好性能： - ）

-

--setup data
declare @t table (VID int, [Datetime] datetime);
insert  @t values
        (1, '1986-01-01 00:00'),    --very early year
        (1, '2016-01-01 00:10'),
        (1, '2016-01-01 00:12'),
        (1, '2016-01-01 00:25'),
        (2, '2016-01-01 00:40'),
        (4, '2016-01-01 01:00'),
        (4, '2016-01-01 02:13'),
        (6, '2016-01-01 02:23'),
        (7, '2016-01-01 02:25'),
        (8, '2016-01-01 02:49'),
        (9, '2016-01-01 02:59'),
        (9, '2016-01-01 03:01'),
        (9, '2016-01-01 03:09'),
        (9, '2016-01-01 03:24'),
        (9, '2016-01-01 04:05');
select  * from @t order by VID, [Datetime];
--select    datediff(MI, (select min([Datetime]) from @t), (select max([Datetime]) from @t));   --15778325 records in 30 years - handled by t4 x t4 x t4 in tally generator

-- Tally generator courtesy of http://www.sqlservercentral.com/blogs/never_say_never/2010/03/19/tally_2D00_table_2D00_cte/
-- Tally Table CTE script (SQL 2005+ only)
-- You can use this to create many different numbers of rows... for example:
-- You could use a 3 way cross join (t3 x, t3 y, t3 z) instead of just 2 way to generate a different number of rows.
-- The # of rows this would generate for each is noted in the X3 comment column below.
-- For most common usage, I find t3 or t4 to be enough, so that is what is coded here.
-- If you use t3 in ‘Tally’, you can delete t4 and t5.
; WITH
    -- Tally table Gen            Tally Rows:     X2                X3
t1 AS (SELECT 1 N UNION ALL SELECT 1 N),    -- 4            ,    8
t2 AS (SELECT 1 N FROM t1 x, t1 y),            -- 16            ,    64
t3 AS (SELECT 1 N FROM t2 x, t2 y),            -- 256            ,    4096
t4 AS (SELECT 1 N FROM t3 x, t3 y),            -- 65536        ,    16,777,216
t5 AS (SELECT 1 N FROM t4 x, t4 y),            -- 4,294,967,296,    A lot
Tally AS (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) N
          FROM t4 x, t4 y, t4 z), -- Change the t3's to one of the other numbers above for more/less rows
--generate time values
Intervals as (
        select  t.N - 1 interval,
                dateadd(mi, (t.N - 1) * 30, min_date.min_date) interval_start,
                dateadd(mi, (t.N) * 30, min_date.min_date) next_interval_start
        from    (
                select  min([Datetime]) min_date
                from    @t
                ) min_date
        join    Tally t
                on  t.N <= datediff(MI, (select min([Datetime]) from @t), (select max([Datetime]) from @t)) / 30 + 1
),
--join intervals to data tables
Intervaled_data as (
        select  *, row_number() over (partition by i.interval order by t.[Datetime]) row_num
        from    @t t
        join    Intervals i
                on  t.[Datetime] >= i.interval_start and t.[Datetime] < i.next_interval_start
)
select  i.VID, i.[Datetime]
from    Intervaled_data i
where   i.row_num = 1
order   by i.VID, i.[Datetime];

光标的另一种选择？

2 个答案: