Database index and hashing

We want to locate where our records are. We might have to resort to index, just like when we are trying to find a key word, we go to the indice in the back of a book.

Basic concepts:

Indices

Indices are used to locate record; Attributes that are used to loop up are called search key. They don’t have to be Key or super key.

Ordered indices: it is based on sorted order of the records

Hash indices

operations and performance affected by choice of indices

Access type:

We can have specific attribute look up or range look up

Space overhead

Deletion

Insert

Ordered indices

Ordered indices are indices that store indices in sorted order.

Clustering indices

Record in the files might themselves be sorted in some order. A clustering index is an index whose search key also defines the sequential order of the file.
They are also called primary index.

Nonclustering indices

Indices order is different from the sequential order of the records. There is a second list that has pointers to the physical rows.

Index entry

It is a search key value and pointer to one or **more than one ** records that has the specific search key value.

Dense index

Index entry appears for every search key value in the file.

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