Can a nondense (sparse) index be used in the implementation of an aggregate operator? Why or why not?
What will be an ideal response?
A nondense (sparse) index contains entries for only some of the search values. A primary index is an example of a nondense index which includes an entry for each disk block of the
data file rather than for every record.
Index File Data File
Key ----------
_____ ---------------> | 10 ... |
| | | | 12 ... |
| 10 | | | 18 ... |
| --|------ ----------
| | -----> ----------
| 22 | | | 22 ... |
| --|--------------- | 28 ... |
| | | 32 ... |
| 40 | ----------
| --|------
|____| | ----------
--------------> | 40 ... |
| 52 ... |
| 60 ... |
----------
If the keys in the index correspond to the smallest key value in the data block then the sparse index could be used to compute the MIN function. However, the MAX function could not be determined from the index. In addition, since all values do not appear in the index, AVG, SUM and COUNT could not be determined from just the index.
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Fill in the blank(s) with correct word
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Answer the following statement true (T) or false (F)