# Retrieving Big Data Quiz - Big Data Integration and Processing
1. **What does it mean for a query language to be declarative?**
* The language specifies the process of how to obtain the data.
* The language specifies what data to obtain.
* A language specific declaration of data types in order to define the method of data retrieval.
* The language specifies both the process of how to obtain the data and specifies what data to obtain.
2. **Use the following table named "user\_table" to answer the next 2 problems.**
userId | username | email |
1 | admin | admin@corporate.moe |
2 | h4xor | 1337@rawr.cte |
*How would you go about querying the entire username column (however many)?*
* SELECT user\_table FROM username
* SELECT username FROM userId WHERE \*
* SELECT username FROM user\_table WHERE userId=1
* SELECT username FROM user_table
3. **How would you go about querying the entire database table (please refer to question 2's table)?**
* SELECT username, email FROM userId
* SELECT *FROM* WHERE user\_table
* SELECT * FROM user_table
* SELECT user\_table FROM \*
4. **What is the global indexing table?**
* An index table in order to keep track of data records within one machine.
* An index table in order to keep track of a given data type that might exist within multiple machines.
* A global table that uses a specific technique called indexing and the table uses an index as the primary key.
* An index table in order to keep track of a given data type that might exist within one machine.
5. **What are the three computing steps of a semi-join?**
* Project, Ship, Reduce
* Project, Decompose, Send
* Index, Join, Display
* Query, Join, Display
* None Applicable
6. **What is the purpose of a semi-join?**
* Increase the speed of the join for trade-off of increased data transmission cost.
* Increase the efficiency of sending data across multiple machines.
* Another name for join: an operation to combine two tables by column.
7. **What is a subquery?**
* A query statement within another query.
* A short query than normal.
* An alternative query that acts as a substitute for another query.
8. **What is a correlated subquery?**
* A type of query that contains a relationship between a variable attribute x and a variable attribute y. The two variables have a dependent relationship causing a correlation.
* A type of query that contains a subquery that requires information from a query one level up.
* A type of query that requires two tables in order to calculate values.
9. **What is the purpose of GROUP BY queries?**
* Enables calculations based on specific columns of the table.
* Required before you can use functions like AVG, SUM, MIN, MAX, COUNT.
* Enables queries within queries.
10. **Consider the following generic statement for questions 10-12:**
`db..find(, ).`
*Which part of the statement would reflect that of the FROM statement in SQL as illustrated in the lecture?*
* <collection>
* <projection>
* <query filter>
* <cursor modifier>
11. **Which part of the statement would reflect that of the SELECT statement in SQL as illustrated in the lecture?**
* <query filter>
* <collection>
* <cursor modifier>
* <projection>
12. **Which part of the statement would reflect that of the WHERE statement in SQL as illustrated in the lecture?**
* <collection>
* <projection>
* <cursor modifier>
* <query filter>
13. **A sample part of the data structure is as follows:**
`{ _id:1, userIndex: 10, email: “arealeamil@notreallu.asd", retainRate:2}`
*What would be the most likely statement that we would need to grab email info for user indexes greater than 24?*
* db.email.find({userIndex:{$gt:24}}, {email:1, _id:0})
* db.userIndex.find({email:{$gt:24}}, {\_id:0})
* db.userIndex.find({email:{$lte:24}}, {\_id:0})
* [db.email](http://db.email).find({userIndex:{$lte:24}}, {email:1, \_id:0})
14. **What does it mean to have a \_id:0 within our query statement?**
* Tell MongoDB not to return a document id.
* Grab as many objects as possible.
* Grab the first object in the results.
* Does not have an effect, simple convention left for compatibility issues.
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