Discussion
An ER model of a database consists of entity types P and Q. These are connected by a relationship R, which does not have its own attributes (i.e., no self attributes).
Under which one of the following condition, can the relational table for R be merged with that of P ?
Answer: C
R can be merged with P when R is many-to-one and the participation of P in R is total.
If R is many-to-one from P to Q, each P entity is related to at most one Q entity. The relationship can then be stored by adding Q's key as a foreign key column in P's table. If P's participation is total, every P row has a value in that column, so no nulls are introduced.
If R is one-to-many from P, a single P entity can relate to many Q entities, which cannot be stored in one row of P; the table would have to merge with Q instead. With partial participation the merged column would hold nulls for P entities outside the relationship.
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