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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 in R and S I. Insert into R II. Insert into S III. Deletion from R IV. Deletion from S Which of the following can cause violation of the relational integrity constraint above?

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 in R and S I. Insert into R II. Insert into S III. Deletion from R IV. Deletion from S Which of the following can cause violation of the relational integrity constraint above? Correct Answer Both II and III

Concept:

  • A foreign key in a table refers to the primary key of another table. It contains a subset of entries of the primary key of another table.
  • It specifies the referential integrity constraint.

Explanation:

Given:

Two relations:

R(a, b, c) and  S(d, e, f)

d is the foreign key of S that refers to the primary key of R

Statement I: Insert into R

It will not cause a violation. Because the inserting element in R will not affect S. Values present in R’s primary key may or may not present in the foreign key of S.

Statement II: Insert into S

It will cause a violation. As d is the foreign key referring to the primary key of R. If we insert values in S, then that value must also be present in the primary key of R and which is not necessary as while inserting in S we are not aware of R.

Statement III: Delete from R

It will cause a violation. If we delete tuples from R relation, then if that tuple is present in S­ which is referring to the primary key of R must also be deleted.

Statement IV: Delete from S

It has no effect on the relation. It will not cause a violation. Values that are deleted from S need not be deleted from R. As S contains the foreign key.

Therefore statement II and statement III will cause violation of the relational integrity constraint

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