SQL Server Space Taken By Empty Strings? -

what penalty in space taken varchar types in sql server 2012 , above? is, if have 3 columns of type nvarchar (or varchar matter), , empty, how space taken in table?

create table dbo.referringurl  (      id int identity(1, 1) not null,      requesturl nvarchar(384) collate sql_latin1_general_cp1_ci_as null,      referringurlname nvarchar(384) collate sql_latin1_general_cp1_ci_as null,      referringipaddress nvarchar(64) collate sql_latin1_general_cp1_ci_as null, ) 

you can test out dbcc page or sql server internals viewer.

some example cases below illustrate following points.

1. a varchar column null or empty takes no space @ except 2 bytes in column offset array (rows 4 , 5).
2. if variable length column null or empty , followed other null/empty values none of these trailing empty columns need 2 bytes in column offset array (rows 6 , 7).
3. if variable length columns null or empty row has no variable length section @ (rows 2 , 3).

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insert dbo.referringurl        (id,         requesturl,         referringurlname,         referringipaddress) values (1,n'aaa','bbb','ccc'),        (2,null,null,null),        (3,'','',''),        (4,null,null,'ccc'),        (5,'','','ccc'),        (6,'aaa',null,null),        (7,'aaa','',''),        (8,n'aaa','bbb','ccc')  

1 - columns have values

the image above sql server internals viewer - helpfully provides key various components in row shown below.

2 - varchar columns null

3 - varchar columns have empty strings

4 - varchar columns null except final one

5 - varchar columns empty except final one

6 - varchar columns null except first one

7 - varchar columns empty except first one

(due bug in internals viewer not highlighting notice same length previous row)