D427 - Database Management Applications TEST with (Q & A) WELL ELABORATED 2024/2025
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D427 - Database Management Applications TEST with (Q & A) WELL ELABORATED 2024/2025
- In some indexes, the pointer also identifies the exact location of the row within the block.
- If an indexed column is unique, the index has one entry for each column value.
- If an indexed column is not ...
D427 - Database Management Applications TEST with
(Q & A) WELL ELABORATED 2024/2025
- In some indexes, the pointer also identifies the exact location of the row within the
block.
- If an indexed column is unique, the index has one entry for each column value.
- If an indexed column is not unique, the index may have multiple entries for some
column values, or one entry for each column value, followed by multiple pointers.
table scan - CORRECT ANSWERa database operation that reads table blocks directly,
without accessing an index.
index scan - CORRECT ANSWERa database operation that reads index blocks
sequentially, in order to locate the needed table blocks.
Hit ratio
When a SELECT query is executed, the database examines the WHERE clause and
estimates hit ratio. If hit ratio is high, the database performs a table scan. If hit ratio is
low, the query needs only a few table blocks, so a table scan would be inefficient.
- Instead, the database:
o Looks for an indexed column in the WHERE clause.
o Scans the index.
o Finds values that match the WHERE clause.
o Reads the corresponding table blocks.
§ If the WHERE clause does not contain an indexed column, the database must
perform a table scan. - CORRECT ANSWERthe percentage of table rows selected by a
query.
binary search
o The database first compares the search value to an entry in the middle of the index.
o If the search value is less than the entry value, the search value is in the first half of
the index. If not, the search value is in the second half.
o The database now compares the search value to the entry in the middle of the
selected half, to narrow the search to one quarter of the index.
o The database continues in this manner until it finds the index block containing the
search value. - CORRECT ANSWERthe database repeatedly splits the index in two
until it finds the entry containing the search value:
, primary index, also called a clustering index - CORRECT ANSWERan index on a sort
column
secondary index, also called a nonclustering index - CORRECT ANSWERan index that
is not on the sort column.
Dense Index - CORRECT ANSWERAn index that contains an entry for every table row.
Sparse Index - CORRECT ANSWERAn index that contains an entry for every table
block.
file organization - CORRECT ANSWERWe refer to the way that we store the data for
subsequent retrieval as the ________ ________.
access method - CORRECT ANSWERThe way that we retrieve the data, based on it
being stored in a particular file organization, is called the _______ ________.
1. The items of interest are copied over into the index but the original text is not
disturbed in any way.
2. The items copied over into the index are sorted (alphabetized in the index at the back
of a book).
3. Each item in the index is associated with a "pointer" (in a book index this is a page
number) pointing to the place in the text where the item can be found. - CORRECT
ANSWERThe index in the back of a book has three key elements that are also
characteristic of information systems indexes:
indexed-sequential - CORRECT ANSWERIn an _________ ___________ file, the file is
stored on the disk in order based on a set of field values (in this case the salesperson
numbers) and an index is built over that same field.
- This allows both sequential and direct access by the key field, which can be an
advantage when applications with different retrieval requirements share the file.
True - CORRECT ANSWERTRUE/FALSE
The simple linear index is not a good solution for indexing the records of a file.
division-remainder - CORRECT ANSWER- In the ____________________________
method of hashing, we divide the key value of the record that we want to insert or
retrieve by the number of record locations that we have reserved.
TRUE - CORRECT ANSWERTRUE/FALSE
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