Calculated Field in SQL Server

A calculated field in SQL Server is a column whose values are computed based on other columns in the same row. You define its logic using an expression.

Why use it?
To derive new information from existing data without storing it permanently. This is useful for:

• Calculating totals, percentages, or ratios.
• Transforming data (e.g., converting units).
• Creating derived values based on multiple columns.

Syntax:

SELECT
    Column1,
    Column2,
    Column3,
    [Calculated Field Name] = Expression
FROM
    TableName;

Example:

SELECT
    OrderDate,
    TotalAmount,
    [Tax Amount] = TotalAmount * 0.08  -- Calculate 8% tax
FROM
    Orders;

Key Points:

• The expression can include columns, constants, and functions.
• Calculated fields are computed when the query is executed.
• They do not store data; they are virtual columns.
• You can use calculated fields in `WHERE`, `GROUP BY`, and `ORDER BY` clauses.