Use the Expression Builder dialog box to create and edit a property expression or write the expression that sets the value of a variable using a graphical user interface that lists variables and provides a built-in reference to the functions, type casts, and operators that the Integration Services expression language includes.
A property expression is an expression that is assigned to a property. When the expression is evaluated, the property is dynamically updated to use the evaluation result of the expression. Likewise, an expression that is used in a variable enables the variable value to be updated with the evaluation result of the expression.
There are many ways to use expressions:
Tasks Update the To line that a Send Mail task uses by inserting an e-mail address that is stored in a variable; or update the Subject line by concatenating a string such as "Sales for: " and the current date returned by the GETDATE function.
Variables Set the value of a variable to the current month by using an expression like DATEPART("mm",GETDATE()); or set the value of a string by concatenating the string literal and the current date by using the expression "Today's date is " + (DT_WSTR,30)(GETDATE()).
Connection Managers Set the code page of a Flat File connection manager by using a variable that contains a different code page identifier; or specify the number of rows in the data file to skip by entering a positive integer like 3 in the expression.
Expand the Variables folder and drag variables to the Expression box.
Expand the folders and drag functions, type casts, and operators to the Expression box.
Edit or type an expression.`
Lists the evaluation result of the expression.
Click Evaluate Expression to view the evaluation result of the expression.