SQL Server PERSISTED Columns (SQL 2005+)
Normal calculated column values are calculated each time a query references them.
Implementing a calculated column as PERSISTED physically stores results in the table.
PERSISTED Calculated Columns
+ Give Better Performance
+ You can create indexes on them
- Take up storage space
ALTER TABLE invoice ADD invoicetotal AS itemtotal + itemtax
PERSISTED Calculated Column
ALTER TABLE invoice ADD invoicetotal AS itemtotal + itemtax PERSISTED
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