Case 1. If there are valid target lookup records in a dictionary for all the corresponding source records, the task picks all the values from the dictionary and replaces in the target.

Case 2. If there are some records in the source for which there are multiple lookup values in a dictionary, the task picks one of the lookup values from the dictionary and substitutes with the source value.

Case 3. if some of the source values are same as the lookup values in a dictionary, the target contains the same data as the source.

Case 4. If the source records do not have a lookup value in a dictionary and if you specify a valid error constant, the task uses the error constant for all the failed lookup conditions.

Case 5. If the source records do not have a lookup value in a dictionary and if you do not specify a valid error constant, the task fails and generates an exception.