Sql query to create graph from a table of events

December 25, 2021

I have a plain old table in SQL Server like so:

JOB    Step     Timestamp
----------------------------------
1      begin    12/25/2021 1:00 AM
1      foo      12/25/2021 1:01 AM
1      bar      12/25/2021 1:02 AM
1      end      12/25/2021 1:03 AM

It is a list of steps, that transition from one to the other, and the transition is determined by the timestamp. I would like to render it as a graph of events, so am trying to query it with results like:

JOB    Source    Target   Timestamp
--------------------------------------------
1      begin     foo      12/25/2021 1:01 AM
1      foo       bar      12/25/2021 1:02 AM  
1      bar       end      12/25/2021 1:03 AM

This is not a SQL Server graph table but I’d like it to behave like one in this case.

This is ultimately going to be rendered in PowerBI using a force directed graph visualization, so answers in T-SQL or DAX would work for my use case.

>Solution :

In t-sql this is simple with lead() window function, the following should produce your expected results

select JOB, [Source], [Target], [TimeStamp]
from (
    select JOB, Step [Source],
        Lead(Step) over(partition by JOB order by [Timestamp]) [Target],
        Lead([Timestamp]) over(partition by JOB order by [Timestamp]) [TimeStamp]
    from t
)t
where [Target] is not null;