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Which of the following is used to delete the entries in the referenced table when the tuple is deleted in course table?
CREATE TABLE course
( . . .
FOREIGN KEY (dept name) REFERENCES department
. . . );
( . . .
FOREIGN KEY (dept name) REFERENCES department
. . . );
- a)Delete
- b)Delete cascade
- c)Set null
- d)All of the mentioned
Correct answer is option 'B'. Can you explain this answer?
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Which of the following is used to delete the entries in the referenced...
The delete “cascades” to the course relation, deletes the tuple that refers to the department that was deleted.
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Which of the following is used to delete the entries in the referenced...
Explanation:
The correct answer is option 'B' (Delete cascade). When a foreign key relationship is established between two tables, it means that the values in the referencing table (course table in this case) are dependent on the values in the referenced table (department table in this case).
When a tuple (row) is deleted from the course table, it may be referencing a tuple in the department table. In such cases, there are different options for handling the deletion:
1. Delete: This option would simply delete the tuple from the course table without affecting the referenced tuple in the department table. This could lead to inconsistencies in the data if the department tuple is still being referenced by other tuples in the course table.
2. Delete cascade: This option ensures that when a tuple is deleted from the course table, any tuples in the department table that are referenced by it will also be deleted. This helps maintain data integrity and ensures that there are no orphaned tuples in the department table.
3. Set null: This option would set the foreign key value in the course table to NULL when the referenced tuple in the department table is deleted. This can be useful in certain scenarios where it is acceptable to have NULL values in the foreign key column.
In this case, the question states that the entries in the referenced table (department table) should be deleted when a tuple is deleted from the course table. Therefore, the correct option is 'Delete cascade' (option B).
In summary, the "Delete cascade" option is used to delete the entries in the referenced table when the tuple is deleted in the course table, ensuring data integrity and avoiding orphaned tuples.
The correct answer is option 'B' (Delete cascade). When a foreign key relationship is established between two tables, it means that the values in the referencing table (course table in this case) are dependent on the values in the referenced table (department table in this case).
When a tuple (row) is deleted from the course table, it may be referencing a tuple in the department table. In such cases, there are different options for handling the deletion:
1. Delete: This option would simply delete the tuple from the course table without affecting the referenced tuple in the department table. This could lead to inconsistencies in the data if the department tuple is still being referenced by other tuples in the course table.
2. Delete cascade: This option ensures that when a tuple is deleted from the course table, any tuples in the department table that are referenced by it will also be deleted. This helps maintain data integrity and ensures that there are no orphaned tuples in the department table.
3. Set null: This option would set the foreign key value in the course table to NULL when the referenced tuple in the department table is deleted. This can be useful in certain scenarios where it is acceptable to have NULL values in the foreign key column.
In this case, the question states that the entries in the referenced table (department table) should be deleted when a tuple is deleted from the course table. Therefore, the correct option is 'Delete cascade' (option B).
In summary, the "Delete cascade" option is used to delete the entries in the referenced table when the tuple is deleted in the course table, ensuring data integrity and avoiding orphaned tuples.
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Which of the following is used to delete the entries in the referenced table when the tuple is deleted in course table?CREATE TABLE course( . . .FOREIGN KEY (dept name) REFERENCES department. . . );a)Deleteb)Delete cascadec)Set nulld)All of the mentionedCorrect answer is option 'B'. Can you explain this answer?
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