Saturday, 10 January 2015

SQL SERVER – Computed Column – PERSISTED and Performance


A computed column is a virtual column that is not physically stored in the table, unless the column is marked PERSISTED. A computed column expression can use data from other columns to calculate a value for the column to which it belongs.

There are two types of computed columns namely persisted and non-persisted.

1. Non-persisted columns are calculated on the fly (ie when the SELECT query is executed) whereas persisted columns are calculated as soon as data is stored in the table.

2. Non-persisted columns do not consume any space as they are calculated only when you SELECT the column. Persisted columns consume space for the data

Example:

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