Using Built-In Functions and Expressions
Now that you have the knowledge to write simple SELECT statements, it is time to explore some of the other features of T-SQL that allow you to manipulate how the data is displayed, filtered, or ordered. To create expressions in T-SQL, you use functions and operators along with literal values and columns. The reasons for using expressions in T-SQL code are many. For example, you may want to display only the year of a column of the DATETIME data type on a report, or you may need to calculate a discount based on the order quantity in an order-entry application. Any time the data must be displayed, filtered, or ordered in a way that is different from how they are stored, you can use expressions and functions to manipulate the results.