16. In typical a hospital, a patient is examined by many doctors and a doctor ex
ID: 3590115 • Letter: 1
Question
16. In typical a hospital, a patient is examined by many doctors and a doctor examines many patients. A database for the hospital has a PATIENTS table whose PK column is Patient-ID and it has a DOCTORS table whose PK column is Doctor-ID. How should these two tables be linked or related? (a) include Patient-ID column in DOCTORS table as a FK column (b) include Doctor-ID column in PATIENTS table as a FK column (c) include a third table in-between PATIENT and DOCTORS table to link the two tables 17. The primary key column of a relational database table must always be the first column in the table: (a) true (b) false 18. In a relational database table, a foreign key column can contain: (a) NULLS or blanks (b) duplicate values (c) both a and b above (d) neither a nor b aboveExplanation / Answer
Answer:
16)
Answer-c
17)
Answer-b
18)
Answer-d
foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table). That is all an FK is by definition. Null by definition is not a value. Null means that we do not yet know what the value is.
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