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DataStax Cassandra Developer Certification Certification Questions and Answer (Dumps and Practice Questions)



Question : You have been given below ER Diagram


What is the correct table design to satisfy below query?

Query: Find all books that is subscribed by a subscriber, subject and support writing year range, with most writing year first
then sorted by title.

: You have been given below ER Diagram
1. A
2. B
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4. D

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Explanation: Please check query first

Find all books that is subscribed by a subscriber and support writing year range, with most writing year first then sorted by
title.


Consider Mapping Rules

Entities and relationships -> e-Book and e-Subscriber
equality search attributes -> subscriber_id, subject
inequiality search attributes -> writing_year
ordering attributes -> writing_year, title
key attributes -> book_id,subscriber_id, subscription_date (because in m to m relationship, we take keys from both the enity as
well as from relationship)





Question : You have been given below conceptual data model


And you have below Access pattern , which of the following is valid table design

where course_name=? and publish_date=?

: You have been given below conceptual data model
1. A
2. B
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4. D

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Explanation: In this case we know, both the attributes are equality operator. Hence, need to be part of primary key
and also they satisfy the uniqueness of the row.





Question : As you know, in Cassandra tables, must have primary keys. For primary key, you can use either TimeUUID or UUID
only?
Which of the following you can say is a Timeuuid?

: As you know, in Cassandra tables, must have primary keys. For primary key, you can use either TimeUUID or UUID
1. 52b11d6d-16e2-4ee2-b2a9-425861b86ab6

2. 1be43390-9fe4-11e3-8d05-425861b86ab6

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4. 1be43390-9fe4-31e3-8d05-425861b86ab6


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Explanation: To differentiate between Time UUID, you need to check third set of data and its first value. If first
value start with 1 than its time UUID and if starts with 4 than its UUID only.

The uuid() function takes no parameters and generates a random Type 4 UUID suitable for use in INSERT or UPDATE statements.

UUID and TIMEUUID are stored the same way in Cassandra, and they only really represent two different sorting implementations.

IMEUUID columns are sorted by their time components first, and then by their raw bytes, whereas UUID columns are sorted by
their version first, then if both are version 1 by their time component, and finally by their raw bytes. Curiosly the time
component sorting implementations are duplicated between UUIDType and TimeUUIDType in the Cassandra code, except for different
formatting.

I think of the UUID vs. TIMEUUID question primarily as documentation: if you choose TIMEUUID you're saying that you're storing
things in chronological order, and that these things can occur at the same time, so a simple timestamp isn't enough. Using
UUID says that you don't care about order (even if in practice the columns will be ordered by time if you put version 1 UUIDs
in them), you just want to make sure that things have unique IDs.

Even if using NOW() to generate UUID values is convenient, it's also very surprising to other people reading your code.

It probably does not matter much in the grand scheme of things, but sorting non-version 1 UUIDs is a bit faster than version
1, so if you have a UUID column and generate the UUIDs yourself, go for another version.



Related Questions

Question : Let's say we want to implement the following schema:

Enity: Staff Member (id , name)
Enity: Permanent (specialises Staff Member) (next_appraisal_date )
Enity: Temporary (specialises Staff Member) (contract_end_date)

a Staff Member is either a Permanent employee or a Temporary contractor. How do you define disjoint in parent child
relationship?
 : Let's say we want to implement the following schema:
1. An entity can only participate in only one subtype role

2. An entity cannot participate in the parent type role

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4. An entity is not complete



Question : The complete flow of a video website is below

1. login to site
2. It will show all recent video channels updated
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This flow is known as
: The complete flow of a video website is below
1. Logical Diagram

2. Application Workflow

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4. Login flow



Question : What is an application workflow?
 : What is an application workflow?
1. All the tasks in an application formed by casual dependencies

2. It is an alternate to ER diagram

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4. It is an alternate to DFD



Question : In Application Workflow Model, how do you define access patterns?
 : In Application Workflow Model, how do you define access patterns?
1. Using access pattern, you determine how data is accessed and you will know, what queries you will be
running.

2. Using access pattern, you determine how data will be arranged in table, so that we can have least
normalization.

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4. 1 and 3

5. 2 and 3



Question : What all are true, with regards to logical model
 : What all are true, with regards to logical model
1. To design logical model use top down approach

2. You can define logical model algorithmically

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4. 1 and 3

5. 1,2 and 3


Question : Conceptual data model is specific to NoSQL databases?
 : Conceptual data model is specific to NoSQL databases?
1. True
2. False