Checks whether the dataset is unidirectional, and if so, raises an EDatabaseError exception.
Returns a Variant with the value false, indicating that a matching record was not found.
Descendant classes that are not unidirectional override this method so that it locates the record where the fields identified by the comma-delimited string KeyFields have the values specified by the Variant or Variant array KeyValues. In classes that implement Lookup, it returns a Variant or Variant array that contains the value or values of the fields specified by the comma-delimited string ResultFields on the specified record.
Select fieldA from Table1 where fieldB = 'C'; ---> Table1->Lookup("fieldB","C","fieldA");