Bits of .NET

Calculating values in application code requires logic duplication. Computed columns calculate automatically in database.

Create Computed Column:

CREATE TABLE Orders (
    OrderId INT PRIMARY KEY,
    Quantity INT,
    PricePerUnit DECIMAL(10,2),
    
    -- Computed column (calculated automatically)
    TotalPrice AS (Quantity * PricePerUnit),
    
    -- Persisted (stored, can be indexed)
    TotalWithTax AS (Quantity * PricePerUnit * 1.1) PERSISTED
);

Automatic Calculation:

INSERT INTO Orders (OrderId, Quantity, PricePerUnit)
VALUES (1, 5, 10.00);

SELECT * FROM Orders;
-- TotalPrice = 50.00 (calculated automatically!)
-- TotalWithTax = 55.00 (calculated and stored)

Full Name Example:

CREATE TABLE Employees (
    FirstName NVARCHAR(50),
    LastName NVARCHAR(50),
    FullName AS (FirstName + ' ' + LastName) PERSISTED
);

-- FullName automatically maintained when FirstName/LastName change!

PERSISTED vs Non-Persisted:
Non-Persisted: Calculated on query (no storage)
PERSISTED: Calculated once, stored (can index, faster queries)