Why alter table <> alter column<> SPARSE does not have an effect in cases 1-3 but only in case 4? I.e. can we say that column can be declared as SPARSE only when creating?
I have tested this code in SQL2012.
-- 1
CREATE TABLE UnSparsed(ID INT IDENTITY(1,1),
FirstCol INT,
SecondCol VARCHAR(100),
ThirdCol SmallDateTime)
GO
INSERT INTO UnSparsed SELECT TOP 50000 NULL,NULL, NULL
FROM master..spt_values v1,
master..spt_values v2
GO
sp_spaceused 'UnSparsed'
GO
--- 2
alter table UnSparsed alter column FirstCol int SPARSE NULL
alter table UnSparsed alter column SecondCol VARCHAR(100) SPARSE NULL
alter table UnSparsed alter column ThirdCol SmallDateTime SPARSE NULL
GO
sp_spaceused 'UnSparsed'
GO
--- 3
truncate table UnSparsed
GO
INSERT INTO UnSparsed SELECT TOP 50000 NULL,NULL, NULL
FROM master..spt_values v1,
master..spt_values v2
GO
sp_spaceused 'UnSparsed'
GO
DROP TABLE UnSparsed
GO
--- 4
CREATE TABLE UnSparsed(ID INT IDENTITY(1,1),
FirstCol INT SPARSE NULL,
SecondCol VARCHAR(100) SPARSE NULL,
ThirdCol SmallDateTime SPARSE NULL)
GO
INSERT INTO UnSparsed SELECT TOP 50000 NULL,NULL, NULL
FROM master..spt_values v1,
master..spt_values v2
GO
sp_spaceused 'UnSparsed'
GO
