来自不同 Historian 表的动态 SQL 查询

Question

I have a historian system in SQL Server which saves certain tag values in a table.

Each month, the system creates a table (partition table) for this historical data as per the below tables.

For example, this table for the month of Feb2021 ( [ sqlt_data_1_2021_02 ] ):

There's another table that owns the partition table's name along with the start and end date for each historical table:

I need to get the data for the historized values in [sqlt_data_x_x_x] based on the start/end date. For example: start Date: 10th of Dec 2020 EndDate: 10th of Feb2021 .

This means the query should first look in the required partition table which, in this case. is [ sqlt_data_1_2021_02], [ sqlt_data_1_2021_01], [ sqlt_data_1_2020_12] .

Then query will retrieve the date from these three tables and UNION ALL for the results.

How can I do this dynamically, since the start & end dates are variable?

I added more clarification about the requirement

--First Query

select  id from sqlth_te where tagpath like '%tagName%' --tagname is Param for SP

 --Result will be ID=153

Second Query end_time and Start_time as parm in SP

SELECT  pname from sqlth_partitions where end_time >=1611489115070 and sqlth_partitions.start_time <= 1612127027358
--result [sqlt_data_1_2021_01] ,[sqlt_data_1_2021_02]

The third Query, use the result of above query which gave table names to

select floatvalue,t_stamp from sqlt_data_1_2021_01  where tagid='153' and t_stamp >=1611489115070--StartDate
union all
select floatvalue,t_stamp from sqlt_data_1_2021_02  where tagid='153'and t_stamp<=1612127027358--EndDate

Sp required Parameters should be [ EXEC SPname 'tagname',end_time,Start_time ]

Answer 1

One option would be to create a dynamic query that picks up all the tables. But it can be error-prone and difficult to debug.

Instead, I think your best bet here is to use dynamic SQL to create a view that contains all the necessary tables aggregated together. We can use a SQL Server Agent job to periodically maintain the view, with this code:

DECLARE @sql nvarchar(max) =
N'CREATE OR ALTER VIEW all_history AS
' +
(SELECT STRING_AGG(
    N'SELECT ' +
    QUOTENAME(p.name, '''') + N' AS name, ' +
    p.start_time + N' AS start_time, ' +
    p.end_time + N' AS end_time, * FROM ' +
    QUOTENAME(p.name)

  , CAST(N'
UNION ALL
' AS nvarchar(max))

FROM sqlth_partitions p
);

-- PRINT @sql;
EXEC (@sql);

Now you will have a view that contains all the data together, and you can query it as normal.

---

If you are using a version of SQL Server that does not have STRING_AGG , you will need the FOR XML PATH method.

I will give you the solution to that also, and we can also show how to do this as a stored procedure instead of a view:

DECLARE @sql nvarchar(max) =
STUFF(
(SELECT
    CAST(NCHAR(10) AS nvarchar(max)) +
    N'UNION ALL' +
    NCHAR(10) +
    N'SELECT ' +
    QUOTENAME(p.name, '''') + N' AS name, ' +
    p.start_time + N' AS start_time, ' +
    p.end_time + N' AS end_time, * FROM ' +
    QUOTENAME(p.name)
FROM sqlth_partitions p
FOR XML PATH(''), TYPE

).value('text()[1]', 'nvarchar(max)'),
1, 11, N'');

-- PRINT @sql;
EXEC (@sql);

As you can see, creating a full query from this is very complex and difficult.

Answer 2

below the answer after getting help from a friend. just share it with the community may it will help.

CREATE PROCEDURE dbo.RetrieveData @tagpath   NVARCHAR(255),

                             @begintime BIGINT,

                             @endtime   BIGINT

AS

DECLARE @tagId VARCHAR(50)



SET @tagId = (SELECT id

              FROM   sqlth_te

              WHERE  tagpath LIKE @tagpath)



DECLARE @PNAME NVARCHAR(100)

DECLARE @SQL NVARCHAR(max)

DECLARE mycursor CURSOR local fast_forward FOR

  SELECT pname AS 'PNAME'

  FROM   sqlth_partitions

  WHERE  end_time >= @endtime

         AND sqlth_partitions.start_time <= @begintime



OPEN mycursor



FETCH next FROM mycursor INTO @PNAME



SET @SQL = ''



WHILE @@FETCH_STATUS = 0

  BEGIN

      SET @SQL = @SQL + 'select floatvalue, t_stamp from '

                 + @PNAME + ' WHERE tagid = ' + @tagId + '  UNION  '



      FETCH next FROM mycursor INTO @PNAME

  END



SET @SQL = LEFT (@SQL, Len(@sql) - 8)



EXEC(@SQL)



IF Cursor_status('global', 'myCursor') >=- 1

  BEGIN

      DEALLOCATE mycursor

  END
go