When you click the Add Variable icon, whatever task or container you select at the time will be the
scope for the variable. Once the scope was set for a variable in the past SQL Server 2005 and 2008
releases, it could not be changed. Now a nice little feature in 2014 is you can change the variable
scope at any time. Some of the additional columns are the Namespace and Raise Event on Variable
Change properties. Lastly, you can select a variable and go to the Properties pane to see extended
properties on the variable. We discuss these properties in more depth in Chapter 3.
You’ll find yourself regularly using system variables throughout your package for auditing or error
handling. Some of the package-scoped system variables that you may find interesting for auditing
purposes are listed in the following table.
Variables are discussed in greater detail in each chapter. For a full list of system variables, please
refer to Books Online under “System Variables.”
Data Flow
Most of your time in SSIS is spent in the Data Flow tab. When you add a Data Flow Task to the
Control Flow design surface, a subsequent Data Flow is created in the Data Flow tab. Whereas a
package has a single Control Flow, it can have many Data Flows. You can expand the Data Flow by
double-clicking the task or by going to the Data Flow tab and selecting the appropriate Data Flow
Task from the top dropdown box (shown in Figure 2-24). In the Data Flow, the key components
are sources, destinations transformations (which appear in the SSIS Toolbox), and paths. Unlike
in the Control Flow, where tasks and containers are connected by precedence constraints that define
the package’s execution workflow; in the Data Flow, sources, transformations, and destinations
are connected by paths that define the flow of data between these components. As you make a
connection, the metadata (information about the columns and their data types) becomes available
to the next component in the Data Flow path. Everything after the source is performed in memory
with a very few exceptions.