Explanation/Reference:
Explanation:
- Sparse columns are ordinary columns that have an optimized storage for null values. Sparse columns reduce the space requirements for null values at the cost of more overhead to retrieve nonnull values.
Consider using sparse columns when the space saved is at least 20 percent to 40 percent.
- A Persisted column would be faster to retrieve.
- A computed column is computed from an expression that can use other columns in the same table. The expression can be a noncomputed column name, constant, function, and any combination of these connected by one or more operators. Unless otherwise specified, computed columns are virtual columns that are not physically stored in the table. Their values are recalculated every time they are referenced in a query. The Database Engine uses the PERSISTED keyword in the CREATE TABLE and ALTER TABLE statements to physically store computed columns in the table. Their values are updated when any columns that are part of their calculation change.
References:
http://msdn.microsoft.com/en-us/library/cc280604.aspx
http://msdn.microsoft.com/en-us/library/ms186241.aspx