Question

I am trying to write a SQL query that links call segments together, dynamicly creating a unique ‘CallID’ column. There are two tables in the database that are used for this, the Call Segment table and the Call Segment Link table which is a One to Many linking table. One call segment can link to many other call segments. Not all call segments have a record in the call segment link table. A call segment link only gets created if the call is transfered.

I am using SQL Server 2008 R2. My ultimate goal is to end up with a query that outputs one row for every Call Segment with one additional column Call ID (the ID of the first call segment).

If anyone has any idea how this would be possible with SQL, I would be very greatful for the help.

Thanks!

Table Structure:
CallSegment
– CallSegmentID

CallSegmentLink
– CallSegmentLinkID
– CallSegmentParentID
– CallSegmentChildID

Answer 1

While sequential call segments admit to processing by CTE, the parallel call segments threw in quite a stumbling block.

The following code will assign call numbers to each call and group the call segments appropriately:

-- Set up the test data.
declare @CallSegments as table ( CallSegmentId int )
insert into @CallSegments ( CallSegmentId ) values ( 1 ), ( 2 ), ( 3 ), ( 4 ), ( 5 ), ( 6 ), ( 7 ), ( 8 )

declare @CallSegmentLinks as table ( ParentCallSegmentId int, ChildCallSegmentId int )
insert into @CallSegmentLinks ( ParentCallSegmentId, ChildCallSegmentId ) values
  ( 1, 2 ), ( 2, 3 ), ( 3, 4 ),
  ( 6, 7 ), ( 6 , 8 )

-- Find all of the   CallSegments   which are not targets of   CallSegmentLinks   and assign a   CallNumber   to each.
declare @Calls as table ( InitialCallSegmentId bit, CallSegmentId int, CallNumber int )
insert into @Calls
  select 1, CallSegmentId, Row_Number() over ( order by CallSegmentId ) as CallNumber
    from @CallSegments
    where not exists ( select 42 from @CallSegmentLinks where ChildCallSegmentId = CallSegmentId )

-- Add the remaining call segments.
insert into @Calls
  select 0, CallSegmentId, NULL
    from @CallSegments
    where CallSegmentId not in ( select CallSegmentId from @Calls )

-- Propogate the   CallNumber   to the remaining call segments.
while ( @@RowCount > 0 )
  begin
  update Child
    set CallNumber = Parent.CallNumber
    from @Calls as Parent inner join
      @CallSegmentLinks as CSL on CSL.ParentCallSegmentId = Parent.CallSegmentId inner join
      @Calls as Child on Child.CallSegmentId = CSL.ChildCallSegmentId
    where Child.CallNumber is NULL and Parent.CallNumber is not NULL
  end

-- Display the grouped call segments with the initial call segment for each call shown first.
select * from @Calls order by CallNumber, InitialCallSegmentId desc, CallSegmentId

Note that the first call segment within each call is flagged. This may help you write additional code that chases through the segments within a call in an order or your own devising.