An expression is a combination of elements that produces a single value. The elements that make up an expression can include variables, literal values, functions and procedures, and operators. An example expression would be 1 < 2, which produces the value true.
While the expression language syntax is derived from the C family of languages, it is not case-sensitive.
Many items in SSIS support expressions. All tasks support expressions for properties, replacing the Dynamic Properties task from DTS. The For Loop and Foreach Loop containers use expressions to specify their looping conditions. See Chapter 4 for more information on these containers. Some tasks, such as the Derived Column task, use expressions to define their output.
Integration Services provides a method of making your tasks dynamic by supporting expressions for task properties.
To view the property expressions for a task, right-click the task and select Edit. This will bring up the task editor window for that task. There will be a list on the left of the different property groupings you can edit. Each task will have an Expressions group that should be the last in the list, as seen in Figure 7-1.
The Expressions property editor will have a plus sign next to it that you can use to expand it to see all the expressions set for any properties. To create ...