Why non-zero values ​​in Sparse columns take up extra space in SQL Server 2008

Question

Can I find out why Sparse columns with non-zero values ​​occupy 4 bytes of extra space. I find out why it takes 4 bytes of extra space . Please help me?

Answer 1

From MSDN (my bold)

The SQL Server Database Engine uses the SPARSE keyword in the definition column to optimize the storage of the value in this column. Therefore, when the column value is NULL for any row in the table, the values ​​do not require storage.

NON-null " " = , :

, , , SPARSE.

.. MSDN +4

, , ?

SPARSE