Please use DISTINCT key word after LOAD statement to avoid the duplicate rows.
TEMP:
LOAD Field1, Field2, Field3 FROM SOURE1;
LOAD Field1, Field2, Field3 FROM SOURE3;
LOAD Field1, Field2, Field3 FROM SOURE3;
FINAL:
Noconcatenate
LOAD DISTINCT * Resident TEMP ;
DROP Table TEMP;