After selecting the source and target databases, you'll see a window specifying the source and target tables. You can change the destination table name or select from the dropdown. To filter columns, define mapping, specify a WHERE condition, or set loading options for an existing target table, click the Columns button as shown below:
Let's click the Columns button for the Orders table:
Now suppose we want to load only orders whose Order Date is on or after 01-14-2014, and skip the EmployeeID column. Click the Source Column dropdown, select Skip for EmployeeID, and specify the WHERE condition:
If the table already exists in subsequent session runs, and we just want to append rows, click the Append Rows option as shown above.
When you click Close, Data Loader automatically checks for any datatype mismatch and validates the WHERE condition.