SQL Server : join records in same table against each other

Question

I have a table which looks like this.

What I want to achieve

1. I want to select the rows that belong together(according to the rules I have provided)

2. I then want to search for F type rows with a date bigger than 2016-01-01 and O type rows which has happened under year 2015.

Sample data:

type        docnr           connection1     connection2    date
F    40195.000000          36950.000000        0.000000    2016-01-29 00:00
O    36950.000000              0.000000    40195.000000    2015-01-29 00:00

As you can see the type of the row determines where the connection to the other lies.

• TYPE F : Connection to the other row is located in connection2
• TYPE O : Connection to the other row is located in connection1

If I were to select all row belonging to each other how would I do that?

So far I have tried to create a self reference to the table

SELECT *
FROM 
   (SELECT  
        faktoofen.datum1 as faktdatum,
        faktoofen.doknr as faktdok,
        ordoofen.doknr as orddok,
        ordoofen.datum1 as orddatum
    FROM 
        [FTG1].[dbo].[oof] as faktoofen,
        [FTG1].[dbo].[oof] as ordoofen
    WHERE 
       (faktoofen.doknr = ordoofen.koppl_dok2 
        OR ordoofen.doknr = faktoofen.koppl_dok1) 
) as subq1
WHERE
    YEAR(subq1.orddatum) = '2015'
    AND YEAR(subq1.faktdatum) = '2016'

This seems a bit clumsy, I can feel a Union would work here but I can't see how.

Answer 1

you might be able to do this using a few cte's and UNION ALL

;WITH TypeF AS 
(
    -- F type rows with a date bigger than 2016-01-01
    SELECT * FROM [FTG1].[dbo].[oof] WHERE [type] = 'F' and [date] >= '2016-01-02'
),
TypeO AS
(
    -- O type rows which has happened under year 2015
    SELECT * FROM [FTG1].[dbo].[oof] WHERE [type] = 'O' and YEAR([date]) = 2015
)

--get only F type rows with matching O type records
SELECT  *
FROM    TypeF
WHERE   [connection1] IN (SELECT    [docnr]
                          FROM      TypeO)
UNION ALL

--get only O type rows with matching F type records
SELECT  *
FROM    TypeO
WHERE   [connection2] IN (SELECT    [docnr]
                          FROM      TypeF)

Answer 2

I think you can get the results with one query with something like below

SELECT *
FROM [FTG1].[dbo].[oof]
where 
(YEAR(subq1.orddatum) = '2015' AND YEAR(subq1.faktdatum) = '2016')
 AND 
(doknr = koppl_dok2 OR doknr = koppl_dok1)