* Storing a null in a sparse column takes up no space at all.
* To any external application the column will behave the same
* Sparse columns work really well with filtered indexes as you will only
want to create an index to deal with the non-empty attributes in the column.
* We can create a column set over the sparse columns that returns an xml
clip of all of the non-null data from columns covered by the set. The
column set behaves like a column itself. Note: you can only have one
column set per table.
* Change Data Capture and Transactional replication both work, but not the
column sets feature.
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