Derived Column (SSIS)

The Derived Column transformation creates new column values by applying expressions to transformation input columns. An expression can contain any combination of variables, functions, operators, and columns from the transformation input. The result can be added as a new column or inserted into an existing column as a replacement value. The Derived Column transformation can define multiple derived columns, and any variable or input columns can appear in multiple expressions.
You can use this transformation to perform the following tasks:

• Concatenate data from different columns into a derived column. For example, you can combine values from the FirstName and LastName columns into a single derived column named FullName, by using the expression FirstName + " " + LastName.
• Extract characters from string data by using functions such as SUBSTRING, and then store the result in a derived column. For example, you can extract a person's initial from the FirstName column, by using the expression SUBSTRING(FirstName,1,1).
• Apply mathematical functions to numeric data and store the result in a derived column. For example, you can change the length and precision of a numeric column, SalesTax, to a number with two decimal places, by using the expression ROUND(SalesTax, 2).
• Create expressions that compare input columns and variables. For example, you can compare the variable Version against the data in the column ProductVersion, and depending on the comparison result, use the value of either Version or ProductVersion, by using the expression ProductVersion == @Version? ProductVersion : @Version.
• Extract parts of a datetime value. For example, you can use the GETDATE and DATEPART functions to extract the current year, by using the expression DATEPART("year",GETDATE()). 

http://msdn.microsoft.com/en-us/library/ms141069.aspx