Thursday, 30 April 2020

DBMS Quiz Questions with Answers 08

Database management systems DBMS TRUE or FALSE questions with answers explained for competitive and entrance exams.


TRUE or FALSE questions in DBMS 


1. When an index is clustered it requires that the data records are sorted in the search key order of the index.
(a) TRUE                                         (b) FALSE
View Answer

Answer: TRUE
What is clustered index?
When a _le is organized so that the ordering of data records is the same as or close to the ordering of data entries in some index, we say that the index is clustered.

2. B+ trees can include duplicate keys.
(a) TRUE                                          (b) FALSE
View Answer

Answer: TRUE
B+ trees can include duplicate keys. A key with row id or key with list of row ids can be used to extend B+ trees with duplicates.

3. When a sparse index is used, each record must have an entry in the index.
                   (a) TRUE                                          (b) FALSE
View Answer

Answer: FALSE
No. Each record need not have an entry in the index table if sparse index is used.
Sparse index is an index in which index record appears for only some of the search-key values. To locate a record, we find the index entry with the largest search-key value that is less than or equal to the search-key value for which we are looking. We start at the record pointed to by that index entry, and follow the pointers in the file until we find the desired record.
Advantages of sparse index are, they require less space, and less maintenance overhead for insertion and deletion of keys.

4. In fixed-length records, a character field of type CHAR is NOT allowed.
                   (a) TRUE                                          (b) FALSE
View Answer

Answer: FALSE
Fixed-length records are records where each record is of same length. Mostly, fixed length records are made up of attribute data types like NUMBER, and CHAR.
CHAR is itself a fixed-length variable. Due to the fixed length property, this variable type does not need terminating NULL and length indicators to mark the size of a word in records.

5. Spanned records refer to records that are longer than blocks and therefore are broken into fragments.
                   (a) TRUE                                          (b) FALSE
View Answer

Answer: TRUE
Spanned records are split into fragments that are distributed over multiple blocks. The portion of a record in one block is refereed as one fragment.
Spanning necessary if records do not fit in a block, e.g. if they have very long fields.
Spanning useful for better space utilization, even if records fit in a block.
Spanned records requires extra header information in records and record fragments such as follows:
- is it fragment? (bit)
- if fragment, is it first or last? (bit)
- if applicable, pointers to previous/next fragment.

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