Question

I need to write a TSQL procedure which would perform 4 selects and join results int one dataset. Can this be done?

P.S.

Selects are performed in a loop

EDIT

Here is the schema. I wan’t to get N latest points from each Unit which belongs to SOME map.

Maps
   Id

Maps2Units
   MapId
   UnitId

Units
   Id

Points
   Id
   UnitId
   Timestamp

Answer 1

Edit: another solution using top

SELECT
    *
FROM
    Maps2Units MU
    CROSS APPLY
    (
    SELECT TOP (@n) --or TOP 3 etc
        *
    FROM
        Points P
    WHERE
        P.UnitId = MU.UnitId
    ) P2

Guessing from your previous comment…

;WITH myCTE AS 
(
    SELECT
        *,
        ROW_NUMBER() OVER (PARTITION BY P.UnitId ORDER BY P.Timestamp DESC) AS PointsRank
    FROM
        Points P
        JOIN
        Maps2Units MU ON P.UnitId = MU.UnitId
)
SELECT
    *
FROM
    myCTE
WHERE
    PointsRank <= @M;

Original:

;WITH myCTE AS 
(
    SELECT
        *,
        ROW_NUMBER() OVER (PARTITION BY SpeciesID ORDER BY AnimalID /* ? */) AS AnimalRank,
        DENSE_RANK() OVER (ORDER BY SpeciesID /* ? */) AS SpeciesRank
    FROM
        MyAnimals
)
SELECT
    *
FROM
    myCTE
WHERE
    SpeciesRank <= @M
    AND
    AnimalRank <= @N