Get next minimum, greater than or equal to a given value for each group

Question

given the following Table1:

    RefID  intVal  SomeVal
    ----------------------
        1      10    val01
        1      20    val02
        1      30    val03
        1      40    val04
        1      50    val05
        2      10    val06
        2      20    val07
        2      30    val08
        2      40    val09
        2      50    val10
        3      12    val11
        3      14    val12
        4      10    val13
        5     100    val14
        5     150    val15
        5    1000    val16

and Table2 containing some RefIDs and intVals like

    RefID  intVal
    -------------
        1      11    
        1      28    
        2       9    
        2      50    
        2      51    
        4      11    
        5       1    
        5     150    
        5     151    

need an SQL Statement to get the next greater intValue for each RefID and NULL if not found in Table1 following is the expected result

    RefID  intVal  nextGt  SomeVal 
    ------------------------------
        1      11      20  val01
        1      28      30  val03
        2       9      10  val06
        2      50      50  val10
        2      51    NULL   NULL
        4      11    NULL   NULL
        5       1     100  val14
        5     150     150  val15
        5     151    1000  val16

help would be appreciated !

Answer 1

Derived table a retrieves minimal values from table1 given refid and intVal from table2; outer query retrieves someValue only.

select a.refid, a.intVal, a.nextGt, table1.SomeVal
from
(
    select table2.refid, table2.intval, min (table1.intVal) nextGt
      from table2
      left join table1
        on table2.refid = table1.refid
       and table2.intVal <= table1.intVal
     group by table2.refid, table2.intval
) a
-- table1 is joined again to retrieve SomeVal 
left join table1
  on a.refid = table1.refid
 and a.nextGt = table1.intVal

Here is Sql Fiddle with live test.

Answer 2

You can solve this using the ROW_NUMBER() function:

SELECT
  RefID,
  intVal,
  NextGt,
  SomeVal,
FROM
  (
    SELECT
      t2.RefID,
      t2.intVal,
      t1.intVal AS NextGt,
      t1.SomeVal,
      ROW_NUMBER() OVER (PARTITION BY t2.RefID, t2.intVal ORDER BY t1.intVal) AS rn
    FROM
      dbo.Table2 AS t2
      LEFT JOIN dbo.Table1 AS t1 ON t1.RefID = t2.RefID AND t1.intVal >= t2.intVal
  ) s
WHERE
  rn = 1
;

The derived table matches each Table2 row with all Table1 rows that have the same RefID and an intVal that is greater than or equal to Table2.intVal. Each subset of matches is ranked and the first row is returned by the main query.

The nested query uses an outer join, so that those Table2 rows that have no Table1 matches are still returned (with nulls substituted for the Table1 columns).

Alternatively you can use OUTER APPLY:

SELECT
  t2.RefID,
  t2.intVal,
  t1.intVal AS NextGt,
  t1.SomeVal
FROM
  dbo.Table2 AS t2
  OUTER APPLY
  (
    SELECT TOP (1)
      t1.intVal
    FROM
      dbo.Table1 AS t1
    WHERE
      t1.RefID = t2.RefID
      AND t1.intVal >= t2.intVal
    ORDER BY
      t1.intVal ASC
  ) AS t1
;

This method is arguably more straightforward: for each Table2 row, get all matches from Table1 based on the same set of conditions, sort the matches in the ascending order of Table1.intVal and take the topmost intVal.