Which of the following commands is correct to delete the values in the…

2023

Which of the following commands is correct to delete the values in the relation teaches?

  1. A.

    Delete from teaches;

  2. B.

    Delete from teaches where Id = Null;

  3. C.

    Remove table teaches;

  4. D.

    More than one of the above

  5. E.

    None of the above

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Show answer & explanation

Correct answer: A

To delete values from a relation (table) in SQL, the correct command is DELETE FROM followed by the table name. Let's analyze each option: Option A: 'Delete from teaches;' — This command deletes all rows from the 'teaches' table. It is syntactically correct and fulfills the requirement to delete values. Option B: 'Delete from teaches where Id = Null;' — This is incorrect because 'Null' should be 'NULL' in SQL. Also, NULL values must be checked using 'IS NULL', not '='. The correct syntax would be 'WHERE Id IS NULL'. Option C: 'Remove table teaches;' — This is invalid because 'Remove' is not a valid SQL command for deleting data. The correct command to delete data is 'DELETE', not 'REMOVE'. Option D: 'More than one of the above' — This is incorrect because only Option A is valid. Options B and C are invalid, so more than one is not correct. Option E: 'None of the above' — This is incorrect because Option A is a valid command to delete values from the 'teaches' table. Therefore, the correct command is Option A.

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