Also, the model does violate two best practices. One best practice is to use VARCHAR2, not CHAR, for storage. You are using CHAR. THe other best practice is to name columns appropriately and to use the proper datatypes for the data that wil be stored. You have columns with '_NO' in the name (HOTEL_NO, ROOM_NO, GUEST_NO). Will those columns hold numeric data or characater data? If numeric data the datatype should be numeric.