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.
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
operations and performance affected by choice of indices
We can have specific attribute look up or range look up
Ordered indices are indices that store indices in sorted order.
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.
Indices order is different from the sequential order of the records. There is a second list that has pointers to the physical rows.
It is a search key value and pointer to one or **more than one ** records that has the specific search key value.
Index entry appears for every search key value in the file.