Question

I know there are a lot of Pivot table examples on the internet, however I’m new to SQL and I’m having a bit of trouble as all the examples seem to be pertaining to aggregate functions.

Table 1:

|Date         | Tag  |Value |
|06/10 2:00pm |  A   |  65  | 
|06/10 2:00pm |  B   |  44  |
|06/10 2:00pm |  C   |  33  |
|06/10 2:02pm |  A   |  12  |
|06/10 2:02pm |  B   |  55  |
|06/10 2:02pm |  C   |  21  |
....
|06/10 1:58am |  A   |  23  |

---

What I would like it to look like is (table 2):

|Date        |  A  |  B  |  C  |
|06/10 2:00pm|  65 |  44 |  33 | 
|06/10 2:02pm|  12 |  55 |  21 | 
.....
|06/10 1:58am| 23 | etc.  | etc. |

(sorry for the format)

Some problems that encounter (doesn’t work with code I have found online)
I’d like to run this as a stored procedure (rather a SQL job), every 2 minutes so that this data from table 1 is constantly being moved to table 2. However I think I would need to alter the date every single time? (thats the syntax I’ve seen)
The pivot table itself seems simple on its own, but the datetime has been causing me grief.
Any code snipets or links would be greatly appreciated.

Thanks.

Answer 1

The pivot itself seems simple:

select *
from table1
pivot (min (Value) for Tag in ([A], [B], [C])) p

As for stored procedure, I would use last date saved in table2 as a filter for table1, excluding incomplete groups (I’m assuming that there will be, at some point, all three tags present, and that only last date can be incomplete. If not, you will need special processing for last date to update/insert a row).

So, in code:

create proc InsertPivotedTags
as
    set NoCount ON
    set XACT_ABORT ON

    begin transaction

    declare @startDate datetime
    -- Last date from Table2 or start of time
    select @startDate = isnull (max ([Date]), '1753-01-01')
      from Table2

    insert into Table2
    select *
      from Table1
     pivot (min (Value) for Tag in ([A], [B], [C])) p
     where [Date] > @startDate
     -- exclude incomplete groups
       and a is not null
       and b is not null
       and c is not null

    commit transaction

If groups can be incomplete you should remove exlude filter and add a delete statement that removes last date in case it is incomplete, and adjusts @startDate to three milliseconds earlier to get the same rows again, but now in more filled up state.