MadeEasy Test Series: Databases - Indexing

Question

Which of the following statement is/are true?

• For any data file it is possible to construct two separate sparse first level indexes on different keys.
• For any data file, it is possible to construct two separate dense first level indexes on different keys.
• For any data file, it is possible to construct a sparse first level index and a dense second level index,both should be useful.
• All the above

Comments

ALL OF THESE .

DENSE MAKE ON NON KEYS SO YES WE CAN MAKE 2 DENSE FIRST LEVEL INDEX

ALSO FOR KEY WE MAKE SPARSE AND FOR NON KEY MAKE DENSE

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how could 1) be true ?

for sparse indexing data file is to be sorted on basis of search key, now creating 2 seperate sparse index means data file must be sorted on 2 different keys, this is likely to be impossible, because we sort on one search key it will become random on another key.

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@Anu ans is 2...

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Sry for previous answer: i didn't see option fully /

1 level index can be sparse or dense but second level index must be sparse . hence 3rd is wrong .

• For any data file, it is possible to construct two separate dense first level indexes on different keys.
• example (A,B,C) A is key now make index on B and C will give you two dense index but both at 1st level.

for 1st option explaination given by nitish

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1 level index can be sparse or dense but second level index must be sparse

can you please explain it?