Question 16 – ISRO-2018

→ The primary index is created for the primary key of a table. So, records are usually clustered according to the primary key. It can be sparse.
→ In the sparse index, index records are not created for every search key. An index record here contains a search key and an actual pointer to the data on the disk. To search a record, we first proceed by index record and reach the actual location of the data. If the data we are looking for is not where we directly reach by following the index, then the system starts a sequential search until the desired data is found.
→ The secondary index usually dense.
→ In the dense index, there is an index record for every search key value in the database. This makes searching faster but requires more space to store index records itself. Index records contain search key value and a pointer to the actual record on the disk.