--Запрос1
SELECT t2.*
FROM dbo.PointParams t1
CROSS APPLY dbo.GetPPRelations1 (t1.ID_PP) t2

--Запрос2
SELECT t2.*
FROM dbo.tt1 t1
CROSS APPLY dbo.GetPPRelations1 (t1.ID_PP) 

CREATE FUNCTION dbo.GetPPRelations1 (@ID_PP int)
RETURNS TABLE 
AS
RETURN
WITH C0 AS
(
SELECT @ID_PP AS ID_PP_Upper
	  ,CAST(0 AS int) AS NUM
	  ,CAST('19000101' AS datetime) AS DT1
	  ,CAST('22000101' AS datetime) AS DT2
UNION ALL
SELECT t1.ID_PP
	  ,CAST(1 AS int) AS NUM
	  ,(CASE WHEN t1.DT1 > t2.DT1 THEN t1.DT1 ELSE t2.DT1 END) AS DT1
	  ,(CASE WHEN t1.DT2 < t2.DT2 THEN t1.DT2 ELSE t2.DT2 END) AS DT2
	FROM dbo.SchemaRealation t1
	JOIN C0 t2 ON t1.ID_Ref = t2.ID_PP_Upper AND t1.DT1 < t2.DT2 AND t1.DT2 > t2.DT1
)
,CTE AS
(
SELECT ID_PP_Upper, DT1, MAX(DT2) AS DT2
	FROM C0 WHERE NUM = 1
GROUP BY ID_PP_Upper, DT1
)
SELECT ID_PP_Upper, MIN(DT1) AS DT1, DT2
	FROM CTE
GROUP BY ID_PP_Upper, DT2
GO

--Содержит 13 617 записей
CREATE TABLE dbo.tt1 (ID_PP int  NOT NULL PRIMARY KEY)

--Содержит 406 774 записей
CREATE TABLE dbo.PointParams (ID_PP int NOT NULL IDENTITY PRIMARY KEY)

--Содержит 386 058 записей
CREATE TABLE dbo.SchemaRealation
(
 ID_PP int NOT NULL
,ID_Ref int NOT NULL
,DT1 datetime NOT NULL
,DT2 datetime NULL
PRIMARY KEY CLUSTERED (ID_PP, ID_Ref, DT1)
)
GO

CREATE UNIQUE NONCLUSTERED INDEX IX_SchemaRealation ON dbo.SchemaRealation (ID_Ref, ID_PP, DT1) INCLUDE (DT2)
GO