Question

我可以用Python（或任何其他语言）相当容易地做到这一点，但我试图看看使用纯T-sql是否可以实现

我有两个表：

表A的每一行都有一堆常规数据和时间戳记

+------+------+------+-----------+
| Col1 | Col2 | Col3 | Timestamp |
+------+------+------+-----------+
| A    | B    | C    | 17:00     |
| D    | E    | F    | 18:00     |
| G    | H    | I    | 23:00     |
+------+------+------+-----------+

表B被视为元数据

+-------+-----------+
| RunNo | Timestamp |
+-------+-----------+
|     1 | 16:50     |
|     2 | 17:30     |
|     3 | 18:00     |
|     4 | 19:00     |
+-------+-----------+

因此，常规数据被引用为“ RunNo”。表B中的时间戳就是在数据库中创建“运行”时的时间戳。您可以通过比较时间戳将常规数据与其正确的运行号进行匹配。例如，表A中第一行的时间戳是17:00，该时间戳大于16:50且小于17:30，因此很显然，该行属于RunNo1。如何执行此查询，因此结果表为< / p>

+------+------+------+-----------+-------+
| Col1 | Col2 | Col3 | Timestamp | RunNo |
+------+------+------+-----------+-------+
| A    | B    | C    | 17:00     |     1 |
| D    | E    | F    | 18:00     |     2 |
| G    | H    | I    | 23:00     |     4 |
+------+------+------+-----------+-------+

虽然我可能在这里使用CASE可能会有所帮助，但我不知道如何将其组合在一起

SELECT a.*,
       CASE WHEN a.TIMESTAMP < b.TIMESAMP AND a.TIMESTAMP > b.TIMSTAMP then b.RunNo END AS RunNo
FROM A as a, B as b

任何帮助将不胜感激。

Answer 1

CASE允许您根据条件返回不同的值（即列或表达式）。这不是你在这里做什么。您要联接表并根据条件过滤匹配的行。

我用Timestamp代替了名字ts，即使逃脱了，我在SQL Fiddle上也遇到了困难。这是一个保留关键字。

SELECT A.Col1, A.Col2, A.Col3, A.ts, MAX(B.RunNo) AS RunNo
FROM
    A
    INNER JOIN B
        ON A.ts > B.ts
GROUP BY A.Col1, A.Col2, A.Col3, A.ts

对于A.ts > B.ts，它为第二项返回RunNo 2。使用A.ts >= B.ts，第二个条目将返回RunNo 3。

请参见http://sqlfiddle.com/#!18/9dd143/6/0

Answer 2

with TableA as (
    Select [Col1] = 'A',[Col2] = 'B',[Col3] = 'C',[Timestamp] = '17:00'
    Union all Select [Col1] = 'D',[Col2] = 'E',[Col3] = 'F',[Timestamp] = '18:00'
    Union all Select [Col1] = 'G',[Col2] = 'H',[Col3] = 'I',[Timestamp] = '23:00'
)
, TableB as (
    Select [RunNo] = '1',[Timestamp] = '16:50'
    Union all Select [RunNo] = '2',[Timestamp] = '17:30'
    Union all Select [RunNo] = '3',[Timestamp] = '18:00'
    Union all Select [RunNo] = '4',[Timestamp] = '19:00'
)
, TableBWithRowNumber as (
    select b.RunNo, ROW_NUMBER() over (order by b.timestamp asc) as number, cast(b.Timestamp as time) as timestamp
    from TableB b
)
, TableBWithNextRun as (
    select b1.RunNo, startTime = b1.timestamp , endTime = b2.timestamp
    from TableBWithRowNumber b1
    left join TableBWithRowNumber b2 on b1.number + 1= b2.number
)
select * 
from TableA a
inner join TableBWithNextRun B 
    on a.Timestamp >= b.startTime and (a.Timestamp < b.endTime or b.endTime is null)

这会将您的时间戳转换为time。我不确定您内部的数据类型是什么。

这将输出以下内容

Col1    Col2    Col3    Timestamp   RunNo   startTime           endTime
A       B       C       17:00       1       16:50:00.0000000    17:30:00.0000000
D       E       F       18:00       3       18:00:00.0000000    19:00:00.0000000
G       H       I       23:00       4       19:00:00.0000000    NULL

Answer 3

您可以使用lag函数来获取列的先验值，然后再进行联接。

WITH Runs AS
(
  SELECT
    RunNo, 
    COALESCE(LAG(TIMESTAMP),'00:00')) AS START_TS,
    TIMESTAMP AS END_TS
  FROM TableB
  ORDER BY RunNo ASC
)
SELECT B.RunNo, A.*
FROM TableA A
JOIN Runs B ON A.Timestamp >= B.Start_TS AND A.Timestamp < B.End_Ts

这应该比大型数据集上的任何按组求解都要快。

基于过滤条件的T-SQL查询列

3 个答案: