When merging data into an existing data table, the first thing you have to decide is whether you are adding new columns or new rows. Then, you must define how the datasets are related. If you are adding new columns of data, you must define the key columns in each table that link the two datasets uniquely for the columns you add. If you are adding new rows of data, you must match or map the column names. When defining key columns and mapping columns, the names that are used in the two tables can be different as long as you know that their values and data types are equivalent.
Adding columns to existing data tables was covered in Chapter 2, It's All About the Data.
Adding rows to an existing data table is straightforward if the column names match. If they don't, you'll need to map them. An example usage of adding rows could...
