Combining SQL Rows

Try this:

SELECT    T1.SrcAddress,    T1.SrcPort,    T1.DestAddress,    T1.DestPort,    T1.Bytes + COALESCE(T2.Bytes, 0) AS TotalBytes,    T1.Bytes AS A_to_B,    COALESCE(T2.Bytes, 0) AS B_to_AFROM (    SELECT SrcAddress, SrcPort, DestAddress, DestPort, SUM(Bytes) AS Bytes    FROM PacketHeaders    GROUP BY SrcAddress, SrcPort, DestAddress, DestPort) AS T1LEFT JOIN (    SELECT SrcAddress, SrcPort, DestAddress, DestPort, SUM(Bytes) AS Bytes    FROM PacketHeaders    GROUP BY SrcAddress, SrcPort, DestAddress, DestPort) AS T2ON T1.SrcAddress = T2.DestAddressAND T1.SrcPort = T2.DestPortAND T1.DestAddress = T2.SrcAddressAND T1.DestPort = T2.SrcPortWHERE T1.SrcAddress < T1.DestAddress OR    (T1.SrcAddress = T1.DestAddress AND T1.SrcPort = T1.DestPort) OR    T2.DestAddress IS NULL

On this test data:

CREATE TABLE PacketHeaders (ID INT, SrcAddress NVARCHAR(100), SrcPort INT, DestAddress NVARCHAR(100), DestPort INT, Bytes INT);INSERT INTO PacketHeaders (ID, SrcAddress, SrcPort, DestAddress, DestPort, Bytes) VALUES(1, '10.0.25.1', 255, '10.0.25.50', 500, 64),(2, '10.0.25.50', 500, '10.0.25.1', 255, 80),(3, '10.0.25.50', 500, '10.0.25.1', 255, 16),(4, '75.48.0.25', 387, '74.26.9.40', 198, 72),(5, '74.26.9.40', 198, '75.48.0.25', 387, 64),(6, '10.0.25.1', 255, '10.0.25.50', 500, 48),(7, '10.0.25.2', 255, '10.0.25.50', 500, 48),(8, '10.0.25.52', 255, '10.0.25.50', 500, 48);

This gives the following results:

'10.0.25.1', 255, '10.0.25.50', 500, 208, 112, 96'10.0.25.2', 255, '10.0.25.50', 500, 48, 48, 0'10.0.25.52', 255, '10.0.25.50', 500, 48, 48, 0'74.26.9.40', 198, '75.48.0.25', 387, 136, 64, 72

The way it works is to first group one-way conversations and total the byte counts. This assures that every conversation will be represented exactly twice - once for each direction. This result is then self-joined to give the result you need, filtering the duplicates by enforcing that the (address, port) of A must be less than B. A left join is used to allow one-way conversations.

I can see two basic ways of doing this...
1. Group it all up, ignoring the a->b and b->a and then self join the results.
2. Rearrange your data with the "lowest" ip address in the 'src' field, but also create a 'direction' field.

Option 2 is probably the way I'd go...

SELECT    SrcAddress,    SrcPort,    DestAddress,    DestPort,    SUM(AtoB) + SUM(BtoA),    SUM(AtoB),    SUM(BtoA)FROM(    SELECT       CASE WHEN SrcAddress < DestAddress THEN SrcAddress  ELSE DestAddress END AS SrcAddress,       CASE WHEN SrcAddress < DestAddress THEN SrcPort     ELSE DestPort    END AS SrcPort,       CASE WHEN SrcAddress < DestAddress THEN DestAddress ELSE SrcAddress  END AS DestAddress,       CASE WHEN SrcAddress < DestAddress THEN DestPort    ELSE ScrPort     END AS DestPort,       CASE WHEN SrcAddress < DestAddress THEN Bytes       ELSE 0           END AS AtoB,       CASE WHEN SrcAddress < DestAddress THEN 0           ELSE Bytes       END AS BtoA    FROM      PacketHeaders)    AS [data]GROUP BY    SrcAddress,    SrcPort,    DestAddress,    DestPort

EDIT

A couple of other answers have version of what I called option 1. I'll have a go at it too rather than spamming comments on people's answers :(

SELECT   ISNULL([AtoB].SrcAddress,  [BtoA].DestAddress)   ISNULL([AtoB].SrcPort,     [BtoA].DestPort)   ISNULL([AtoB].DestAddress, [BtoA].SrcAddress)   ISNULL([AtoB].DestPort,    [BtoA].SrcPort)   ISNULL([AtoB].Bytes,0) + ISNULL([BtoA].Bytes,0),   ISNULL([AtoB].Bytes,0),   ISNULL([BtoA].Bytes,0)FROM   (      SELECT   SrcAddress, SrcPort, DestAddress, DestPort, SUM(Bytes) AS Bytes      FROM     PacketHeaders      WHERE    SrcAddress <= DestAddress      GROUP BY SrcAddress, SrcPort, DestAddress, DestPort   )   AS [AtoB]FULL OUTER JOIN   (      SELECT   SrcAddress, SrcPort, DestAddress, DestPort, SUM(Bytes) AS Bytes      FROM     PacketHeaders      WHERE    SrcAddress > DestAddress      GROUP BY SrcAddress, SrcPort, DestAddress, DestPort   )   AS [BtoA]      ON  [AtoB].SrcAddress  = [BtoA].DestPort      AND [AtoB].SrcPort     = [BtoA].DestAddress      AND [AtoB].DestAddress = [BtoA].SrcPort      AND [AtoB].DestPort    = [BtoA].SrcAddress

But I did say I wouldn't do it that way...