SQL Expression Is a combination of symbols and operators which are used by the SQL Server Database Engine to evaluates and obtain a single data value. Simple expressions can be a single constant, variable, column, or scalar function. Operators can be used to join two or more simple expressions into a complex expression. SQL Expression always evaluates to a single result an in there a Transact-SQL. A single SQL Expression may have a different value in each row of the result set but each row has only one value for the expression. SQL Expression is work as functional arguments which is used for reusable codes.