MadeEasy Test Series: Databases - Indexing

Question

#DBMS

Which of the following statements is/are true?

(A) For any data file it is possible to construct two separate sparse first level indexes on different keys.

(B) For any data file, it is possible to construct two separate dense first level indexes on different keys.

(C) For any data file, it is possible to construct a sparse first level index and a dense second level index both should be useful.

Comments

Only B Should be the answer. Assumption if there are $2$ candidate keys in data file data is not organized with respect to both of them rare but possible though for ex : Serial Number and Student Id

For C ) Making second level dense index is wastage of memory because simply making it sparse can also work the same.

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what if we make two sparse index based on those keys? @saxena0612

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@saxena0612

Suppose both serial no and student Id combined is a key. Then I think it is possible to construct sparse indexing on each of them separately. Correct me if I am wrong.

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@ Abhishek Kumar Singh,@ Bad_Doctor

Can't get you both ! Spare index is always meant for blocks and i gave an exception which should not consider here because its not a generalize case.

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I was saying that suppose both serial ID and student ID together is a key. So some of the values of serial ID may be repeating and some of the values of student ID may be repeating. Now I made a sparse index on student ID by pointing to first pointer to first unique value second pointer to second unique value of student ID and so on. In this way we can get a sparse index pointing to each block of student ID. Similarly for serial ID.

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I think both (A) and (B) are possible, while option (C) doesn't make any sense.