Computer Science Engineering (CSE) Exam > Computer Science Engineering (CSE) Questions > Let R1(a,b,c) and R2(x,y,z) be two relations ...
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Let R1(a,b,c) and R2(x,y,z) be two relations in which a is the foreign key of R1 that refers to the primary key of R2.
Consider the following four options:
Which of the following is/are correct about the referential integrity constraint?
- a)Insert into R1 will cause violation.
- b)Insert into R2 will cause violation.
- c)Delete from R1 will cause violation.
- d)Delete from R2 will cause violation.
Correct answer is option 'A,D'. Can you explain this answer?
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Most Upvoted Answer
Let R1(a,b,c) and R2(x,y,z) be two relations in which a is the foreign...
A foreign key in a table refers to the primary key of another table. It contains subset of entries of primary key of other table. It specifies the referential integrity constraint.
Given,
Two relations:
R1(a,b,c) and R2(x,y,z)
a is the foreign key of R1 that refers to the primary key of R2.
Option (A): Insert into R1
It will cause a violation. As a is the foreign key referring to the primary key of R2. If we insert values in R1, then that value must also be present in the primary key of R2 and which is not necessary as while inserting in R1 we are not aware of R2.
Option (B): Insert into R2
It will not cause a violation. Because the inserting element in R2 will not effect R1. Values present in R2's primary key may or may not present in the foreign key of R1.
Option (C): Delete from R1
It has no effect on the relation. It will not cause a violation. Values that are deleted from R1 need not be deleted from R2. As R1 contains the foreign key.
Option (D): Delete from R2
It will cause a violation. If we delete tuples from R2 relation, then if that tuple is present in R1 which is referring to the primary key of R2 must also be deleted.
Hence, the correct options are (A) and (D).
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Community Answer
Let R1(a,b,c) and R2(x,y,z) be two relations in which a is the foreign...
Referential integrity constraint and its impact on the relations R1 and R2:
Referential integrity is a concept in relational databases that ensures the consistency and correctness of data relationships between tables. In this scenario, R1(a, b, c) is a relation with a foreign key 'a' that references the primary key of R2(x, y, z). Let's analyze the impact of referential integrity constraint on the given options:
a) Insert into R1 will cause violation:
- This option is correct because when inserting a new row into R1, the value of the foreign key 'a' must exist as a primary key in R2. If the value of 'a' does not exist in R2, it will violate the referential integrity constraint.
b) Insert into R2 will cause violation:
- This option is incorrect because inserting a new row into R2 does not directly impact the referential integrity constraint. It is the insertion into R1 that needs to ensure the integrity by referencing an existing primary key in R2.
c) Delete from R1 will cause violation:
- This option is incorrect because deleting a row from R1 does not violate the referential integrity constraint. However, if a row is deleted from R2 that is referenced by the foreign key 'a' in R1, it will cause a violation unless the referential integrity constraint is set to cascade delete.
d) Delete from R2 will cause violation:
- This option is correct because if a row is deleted from R2 that is being referenced by the foreign key 'a' in R1, it will cause a violation of the referential integrity constraint. The referential integrity constraint ensures that the foreign key in R1 always refers to an existing primary key in R2.
In summary, the correct options are 'a) Insert into R1 will cause violation' and 'd) Delete from R2 will cause violation'. Inserting a row into R1 requires a valid primary key from R2, and deleting a row from R2 that is referenced by R1 violates the referential integrity constraint.
Referential integrity is a concept in relational databases that ensures the consistency and correctness of data relationships between tables. In this scenario, R1(a, b, c) is a relation with a foreign key 'a' that references the primary key of R2(x, y, z). Let's analyze the impact of referential integrity constraint on the given options:
a) Insert into R1 will cause violation:
- This option is correct because when inserting a new row into R1, the value of the foreign key 'a' must exist as a primary key in R2. If the value of 'a' does not exist in R2, it will violate the referential integrity constraint.
b) Insert into R2 will cause violation:
- This option is incorrect because inserting a new row into R2 does not directly impact the referential integrity constraint. It is the insertion into R1 that needs to ensure the integrity by referencing an existing primary key in R2.
c) Delete from R1 will cause violation:
- This option is incorrect because deleting a row from R1 does not violate the referential integrity constraint. However, if a row is deleted from R2 that is referenced by the foreign key 'a' in R1, it will cause a violation unless the referential integrity constraint is set to cascade delete.
d) Delete from R2 will cause violation:
- This option is correct because if a row is deleted from R2 that is being referenced by the foreign key 'a' in R1, it will cause a violation of the referential integrity constraint. The referential integrity constraint ensures that the foreign key in R1 always refers to an existing primary key in R2.
In summary, the correct options are 'a) Insert into R1 will cause violation' and 'd) Delete from R2 will cause violation'. Inserting a row into R1 requires a valid primary key from R2, and deleting a row from R2 that is referenced by R1 violates the referential integrity constraint.
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Let R1(a,b,c) and R2(x,y,z) be two relations in which a is the foreign key of R1 that refers to the primary key of R2.Consider the following four options:Which of the following is/are correct about the referential integrity constraint?a)Insert into R1 will cause violation.b)Insert into R2 will cause violation.c)Delete from R1 will cause violation.d)Delete from R2 will cause violation.Correct answer is option 'A,D'. Can you explain this answer?
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