-- кластеризованная таблица
CREATE TABLE dbo.t_sample_clustered 
(
	[ID] INT IDENTITY(1,1) NOT NULL,
	A INT NOT NULL,
	B INT NOT NULL 
	CONSTRAINT [PK_t_sample_clustered] PRIMARY KEY CLUSTERED([ID] )
)

INSERT INTO dbo.t_sample_clustered  (a,b)
SELECT	TOP 1000000 
		ABS(CONVERT(INT, (CONVERT(BINARY(4), (NEWID()))))) % 1000 AS a,
		ABS(CONVERT(INT, (CONVERT(BINARY(4), (NEWID()))))) % 1000 AS b
FROM sysobjects A
CROSS JOIN sysobjects B
CREATE NONCLUSTERED INDEX [IDX_t_sample_clustered_a] ON dbo.t_sample_clustered (a)

UPDATE STATISTICS dbo.t_sample_clustered  WITH FULLSCAN

-- куча
CREATE TABLE dbo.t_sample 
(
	[ID] INT IDENTITY(1,1) NOT NULL,
	A INT NOT NULL,
	B INT NOT NULL 
	CONSTRAINT [PK_t_sample] PRIMARY KEY NONCLUSTERED([ID] )
)
-- заполнение
INSERT INTO dbo.t_sample  (a,b)
SELECT	A,B
FROM dbo.t_sample_clustered 
-- 
CREATE NONCLUSTERED INDEX [IDX_t_sample_a] ON dbo.t_sample (a)


UPDATE STATISTICS dbo.t_sample  WITH FULLSCAN

SELECT t.b
FROM dbo.t_sample_clustered t
WHERE t.a = 45

SELECT t.b
FROM dbo.t_sample t
WHERE t.a = 45