database-indexing-2

Question

Maximum number of clustered indices one can build for a table with n attributes, which already has a primary index?

Answer 1

a table or the keys can have atmost one primary or clustered index....as there is already a primary index it cannot have clustered index....actually this is due to physical ordering which can be done only in one way.

Answer 2

I assume that by primary index, you mean index on a single attribute.

Without even primary index,

total indexes = nC1 + nC2............nCn   (you can build index on any no of attribtes like our dictionary)

But nC1 is already used.So we need to subtract from the final answer.

Now, nC0 + nC1 + nC2............nCn =2ⁿ

Thus, answer = 2ⁿ - nC1 - nC0 = 2ⁿ -(n+1)

Comments

answer is given 0, i dont know why.

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In order that we have a clsutered index, its necessary that we choose some attributes from the 'n' attributes, sort the table as per these choosen attributes and build an index like a dictionary's index immediately after the preface based on these choosen attributes.

Now, what I feel is sorting the table as per these choosen attributes might break the order of data in table which is required by the primary indexing.

So, answer may be 0. But we know nothing about the data in the table.

So, this is confusing for me.