Combining multiple rows into one single row

Question

I have a table structure like this one:

I need to get the latest values of each column != NULL. My current approach is to use a UNION statement like this one:

SELECT TOP 1 testlong1_min, testlong1_max, NULL, NULL, NULL, NULL, NULL, NULL FROM Grenzwerte WHERE testlong1_min IS NOT NULL AND testlong1_max IS NOT NULL UNION 
SELECT TOP 1 NULL, NULL, testlong2_min, testlong2_max, NULL, NULL, NULL, NULL FROM Grenzwerte WHERE testlong2_min IS NOT NULL AND testlong2_max IS NOT NULL UNION 
SELECT TOP 1 NULL, NULL, NULL, NULL, testlong3_min, testlong3_max, NULL, NULL FROM Grenzwerte WHERE testlong3_min IS NOT NULL AND testlong3_max IS NOT NULL UNION 
SELECT TOP 1 NULL, NULL, NULL, NULL, NULL, NULL, testlong4_min, testlong4_max FROM Grenzwerte WHERE testlong4_min IS NOT NULL AND testlong4_max IS NOT NULL 

This doesn't seem to work, my result is empty. I also thought about doing 1 query per field, but I guess that'll be too much of an overhead compared to the UNION-statement.

Question:

Is there a way to concenate the columns and return the latest values in one row?

EDIT

Using Parodo's suggestion I now get this result, now I need to combine the rows into one.

Answer 1

You should use is not null instead of <> NULL as below

SELECT TOP 1 testlong1_min, testlong1_max, NULL, NULL, NULL, NULL, NULL, NULL FROM Grenzwerte WHERE testlong1_min IS NOT NULL AND testlong1_max IS NOT NULL 
UNION 
SELECT TOP 1 testlong1_min, testlong1_max, NULL, NULL, NULL, NULL, NULL, NULL FROM Grenzwerte WHERE testlong1_min IS NOT NULL AND testlong1_max IS NOT NULL 
UNION 
SELECT TOP 1 NULL, NULL, testlong2_min, testlong2_max, NULL, NULL, NULL, NULL FROM Grenzwerte WHERE testlong2_min IS NOT NULL AND testlong2_max IS NOT NULL 
UNION 
SELECT TOP 1 NULL, NULL, NULL, NULL, testlong3_min, testlong3_max, NULL, NULL FROM Grenzwerte WHERE testlong3_min IS NOT NULL AND testlong3_max IS NOT NULL 
UNION 
SELECT TOP 1 NULL, NULL, NULL, NULL, NULL, NULL, testlong4_min, testlong4_max FROM Grenzwerte WHERE testlong4_min IS NOT NULL AND testlong4_max IS NOT NULL 

Be careful with UNION because it eliminates duplicates. If you want to see duplicates use UNION ALL instead.

Answer 2

In the bellow statement, each CTE will have all the respective non null couples only and will also get a row number where the latest id will have number 1. So then i only get the latest id based on rownumber for each CTE, so each will have only one row. That way CROSS JOINING will result in a single row having the needed results.

;WITH testLong1CTE AS
(
    SELECT testlong1_min, testlong1_max, ROW_NUMBER()OVER(ORDER BY ID DESC) AS rn
    FROM   Table
    WHERE  testlong1_min IS NOT NULL AND testlong1_max IS NOT NULL
),testLong2CTE AS
(
    SELECT testlong2_min, testlong2_max, ROW_NUMBER()OVER(ORDER BY ID DESC) AS rn
    FROM   Table
    WHERE  testlong2_min IS NOT NULL AND testlong2_max IS NOT NULL
),testLong3CTE AS
(
    SELECT testlong3_min, testlong3_max, ROW_NUMBER()OVER(ORDER BY ID DESC) AS rn
    FROM   Table
    WHERE  testlong3_min IS NOT NULL AND testlong3_max IS NOT NULL
),testLong4CTE AS
(
    SELECT testlong4_min, testlong4_max, ROW_NUMBER()OVER(ORDER BY ID DESC) AS rn
    FROM   Table
    WHERE  testlong4_min IS NOT NULL AND testlong4_max IS NOT NULL
)
SELECT testlong1_min, 
       testlong1_max,
       testlong2_min, 
       testlong2_max,
       testlong3_min, 
       testlong3_max,
       testlong4_min, 
       testlong4_max
FROM (SELECT testlong1_min, testlong1_max FROM testLong1CTE WHERE rn = 1) AS T1
CROSS JOIN (SELECT testlong2_min, testlong2_max FROM testLong2CTE WHERE rn = 1) AS T2
CROSS JOIN (SELECT testlong3_min, testlong3_max FROM testLong3CTE WHERE rn = 1) AS T3
CROSS JOIN (SELECT testlong4_min, testlong4_max FROM testLong4CTE WHERE rn = 1) AS T4

Answer 3

When you combine two queries using UNION operator, the resulting resultset is the unique rows from the concatenation of both queries and that's not what you intend. If you want a single row with the latest non-null values for each column you should first get the latest non-null values and join every column into the result.

; WITH
tab1 AS (
   SELECT TOP 1 testlong1_min, testlong1_max
   FROM Grenzwerte
   WHERE testlong1_min IS NOT NULL
   ORDER BY [mySequenceColumn]
),
tab2 AS (
   SELECT TOP 1 testlong2_min, testlong2_max
   FROM Grenzwerte
   WHERE testlong2_min IS NOT NULL
   ORDER BY [mySequenceColumn]
),
tab3 AS (
   SELECT TOP 1 testlong3_min, testlong3_max
   FROM Grenzwerte
   WHERE testlong3_min IS NOT NULL
   ORDER BY [mySequenceColumn]
),
tab4 AS (
   SELECT TOP 1 testlong4_min, testlong4_max
   FROM Grenzwerte
   WHERE testlong4_min IS NOT NULL
   ORDER BY [mySequenceColumn]
),
SELECT *
FROM tab1 CROSS JOIN tab2 CROSS JOIN tab3 CROSS JOIN tab4;