A column is computed from an expression
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.
Create table with a computed column
Create table NetProfit ( SalaryToEmployee int, BonusDistributed int, BusinessRunningCost int, BusinessMaintenanceCost int, BusinessEarnings int, BusinessNetIncome As BusinessEarnings - (SalaryToEmployee + BonusDistributed + BusinessRunningCost + BusinessMaintenanceCost ) )
Value is computed and stored in the computed column automatically on inserting other values.
Insert Into NetProfit (SalaryToEmployee, BonusDistributed, BusinessRunningCost, BusinessMaintenanceCost, BusinessEarnings) Values (1000000, 10000, 1000000, 50000, 2500000)
Simple example we normally use in log tables
CREATE TABLE [dbo].[ProcessLog]( [LogId] [int] IDENTITY(1,1) NOT NULL, [LogType] [varchar](20) NULL, [StartTime] [datetime] NULL, [EndTime] [datetime] NULL, [RunMinutes] AS (datediff(minute,coalesce([StartTime],getdate()),coalesce([EndTime],getdate())))
This gives run difference in minutes for runtime which will be very handy..