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Let $R (a, b, c)$ and $S(d, e, f)$ be two relations in which $d$ is the foreign key of $S$ that refers to the primary key of $R$. Consider the following four operations $R$ and $S$

1. Insert into $R$

2. Insert into $S$

3. Delete from $R$

4. Delete from $S$

Which of the following can cause violation of the referential integrity constraint above?

1. Both I and IV

2. Both II and III

3. All of these

4. None of these

ans:-B

Rule of thumb => In PARENT it’s Update and Delete , In CHILD it’s Update and Insert.

$$\overset{R}{\begin{array}{|c|c|c|} \hline \textbf {a (PK)} & \textbf {b} & \textbf {c} \\\hline \text{1} \\\hline \text{2} \\\hline \end{array}} \qquad \overset{S}{\begin{array}{|c|c|c|} \hline \textbf {d (FK referring to PK of R)} & \textbf {e} & \textbf{f} \\\hline \text{2} \\\hline \text{1} \\\hline \end{array}}$$

• Insert into $R$ cannot cause any violation.
• Insert into $S$ can cause violation if any value is inserted into d of S, which value is not in a of R.
• Delete from $S$ cannot cause any violation.
• Delete from $R$ can cause violation if any tuple is deleted, and as a result a value in 'a' gets deleted which is referenced to by 'd' in $S.$

Correct Answer: $B$

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### 1 comment

This question build my referential integrity constraint concept very well
2-Insert into S   and  3-Delete from R  ,can cause Violation of the Referential integrity constraints.

Hence ,ans  is  (B) Both II and III
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