no sql

Question 1

what are the 4 types of data

Answer 1

structured and unstructured
dynamic and static

Question 2

dynamic

Answer 2

changing frequently

Question 3

static

Answer 3

never changes

Question 4

strcutured

Answer 4

formal predefined
easy to store and process

Question 5

unstructured

Answer 5

e.g. audio, image, music
usually still has internal structural properties

Question 6

sharding data

Answer 6

splitting the data to allow concurrent/parallel access using multiple machines
can simultaneously access each shard

Question 7

in which two ways can we scale databases

Answer 7

vertically and horizontally

Question 8

vertical scaling

Answer 8

upgrading hardware e.g. increasing memory

Question 9

what is the limitaiton of vertical scaling

Answer 9

limited by the amount of cpu ram disk etc that can be configured on a single machine

Question 10

horizontal scaling

Answer 10

adding more machines which requires shading and replication so you can work with them simultaneously

Question 11

what is the limitation of horizontal scaling

Answer 11

read-to-write ratio and communication overhead

Question 12

in which three ways can we benefit form parallelisation

Answer 12

maximise the fraction of the program that can be parallelised
balance the work load and parallel process
minimise the time spent on communication

Question 13

how does the two phase commit protocol work

Answer 13

the coordinator requests cote for commit and the participants either approve or reject
if all participants accept then everything gets committed at the same time

Question 14

what is the issue with two phase commit

Answer 14

hard to find a time where all servers are ready to commit

Question 15

what is the CAP theorem

Answer 15

any distributed database with shared data can have at most 2/3
usually sacrificing consistency

Question 16

what are the three components of cap theorem

Answer 16

consistency; every node always sees the same data at the same time
availability; the system continues operating even if nodes crash or software or hardware is down
partition tolerance; the system works well when distributed

Question 17

what are the BASE properties

Answer 17

basically available; the system guaranteed availability
soft state; system state may change over time
eventual consistency; will eventually become consistent

Question 18

what does it mean for a db to be eventually consistent

Answer 18

if all replicas will gradually become consistent in the absence of updates

Question 19

what makes no sql no sql

Answer 19

no strict schema requirements
no strict adherence to acid properties
consistency is traded in favour of availability

Question 20

document database/store

Answer 20

loosely structured set of key value pairs in documents encapsulate and encode data in some standard formats/encodings
treated as a whole
query languages can help retrieve documents based on their contents
addressed in the db via the unique key

Question 21

in mongo what is the primary key

Answer 21

key; “_id”

Question 22

sorted ordered column-oriented stores

Answer 22

columns are grouped in column families which data is stored in rather than tables
each unit of data is a set of key value pairs identified by row-key

Question 23

graph db

Answer 23

everything is stored as an edge node or attribute
each node and edge can have any number attributes and can be labelled which narrows searches

Question 24

what do document db use instead of an fk

Answer 24

embedded documents and referencing

Question 25

what can be a value in document db

Answer 25

any data type

Question 26

references

Answer 26

including links from one document in another which normalises the db

Question 27

what are some benefits of using referencing

Answer 27

can represent more complex many-to-many relationships good for large hierarchical datasets

Question 28

what is a negative of using referencing

Answer 28

requires follow up queries to find all the data you need

Question 29

embedded data

Answer 29

having a doc inside another via an array

Question 30

embedded data positive

Answer 30

can get all the data in one call using less queries

Question 31

negative of embedded data

Answer 31

the db isn't normalised an not all values are atomic

Question 32

data model

Answer 32

displays a set of tables and the relationship between them providing a blueprint so you can identify which data is important and what should be maintained

Question 33

which two parts of the CAP approach does mongodb focus on

Answer 33

consistency and partition tolerance

Question 34

what are the different parts of the mongodb structure and how do they relate to eachother

Answer 34

an instance has 0/more databases a database has 0/more collections a collection has 0/more documents a document has 1/more fields/attributes

Question 35

what is mongosh

Answer 35

an interactive shell that is a fully functional javascrips interpreter

Question 36

in mongo what happens when you USE a db but it doesnt exist

Answer 36

mongo creates it

Question 37

db.dropDatabase

Answer 37

deleted the db

Question 38

show dbs

Answer 38

shows your databases

Question 39

what does db.collection.findOne({"title": /c/}) do

Answer 39

finds all the attributes with c in the name (regular expressions)

Question 40

mongod

Answer 40

db instance

Question 41

CRUD

Answer 41

create read update delete

Question 42

db.collection.insertOne()

Answer 42

inserts a single document into the collection and if the collection doesnt exist then mongo creates it

Question 43

what does the backtick do``

Answer 43

evaluates the contents within it

Question 44

db.collection.find

Answer 44

prints all docs in the collection

Question 45

db.collection.find()

Answer 45

prints all docs in the collection that match the query

Question 46

db.collection.find().count

Answer 46

prints the number of docs in the collection that match the query

Question 47

db.collection.findOne()

Answer 47

prints the first doc that matches the query

Question 48

what happens if the projection and query are both null (db.collection.findOne(,)

Answer 48

prints out all the fields in the first document

Question 49

db.collection.updateOne((,)

Answer 49

updates the command matching the query

Question 50

db.collection.updateMany((,)

Answer 50

updates all documents matching the query

Question 51

in which two ways do we enforce constraints in mongodb

Answer 51

validators and indexes

Question 52

validator

Answer 52

ensure fields meet specific criteria e.g. required, not null, datatype

Question 53

indexes

Answer 53

can enforce uniqueness and speeds up searching by organising data and provide multiplicity constraints e.g. unique

Question 54

index 1

Answer 54

ascending

Question 55

index -1

Answer 55

descending

Question 56

how do we use indexes to create m:n relationships

Answer 56

creating a compound index for the join table and make them unique

Question 57

validator + index

Answer 57

exactly 1

Question 58

using index means

Answer 58

at most one

Question 59

using validator means

Answer 59

at least one

Question 60

what is the main difference between validators and indexes when being created

Answer 60

validators are created while creating the collection whilst indexes can be created after

Question 61

what is the key symbol for a query

Answer 61

$

Question 62

$gt

Answer 62

greater than

Question 63

$eq

Answer 63

equal

Question 64

$and

Answer 64

AND

Question 65

$or

Answer 65

OR

Question 66

$regex

Answer 66

regular expression

Question 67

what does {} signify in a findOne()

Answer 67

the condition

Question 68

how can we ensure total participation using a validator

Answer 68

required: [x,y]

Question 69

,

Answer 69

implicit AND

Question 70

what does a regex start and end with

Answer 70

/ and $/

Question 71

^ meaning in regex

Answer 71

start of the string

Question 72

. meaning in regex

Answer 72

any character

Question 73

{5,} meaning in regex

Answer 73

at least 5

Question 74

i meaning in regex

Answer 74

case insensitive

Question 75

?! meaning in regex

Answer 75

negative lookahead; checks if the pattern does not follow the current position

Question 76

?= meaning in regex

Answer 76

positive lookahead; checks if the pattern follows the current position

Question 77

* meaning in regex

Answer 77

order of string not important

Question 78

what is the cursor in mongodb

Answer 78

a pointer that keeps the value returned by find()

Question 79

how do you retrieve documents as a constant value from the cursor

Answer 79

using loops

Question 80

.sort({item: 1/-1})

Answer 80

sorts the returned items in ascending or descending order

Question 81

how do we show which attributes we want to be included in the result of find()

Answer 81

at the v end of the query name: 1

Question 82

how do we omit the _id from our find() result

Answer 82

_id: 0 can only be used with _id as its automatically given

Question 83

how do we use IN in mongodb

Answer 83

type: {$in:['food']}

Question 84

how do we search in an embedded document

Answer 84

need to fill all subdocuments fields and in the same order when making your query

Question 85

how do we get the first value in an array when writing a query

Answer 85

e.g. 'ratings.0'

Question 86

what does $elemMatch do

Answer 86

returns if at least one array element satisfies the entire condition

Question 87

why do we need to use $elemMatch

Answer 87

if we dont and we have multiple conditions then mongo just does an implicit or

Question 88

what is the mongo equivalent of group by having

Answer 88

$group $match

Question 89

aggregation pipeline

Answer 89

documents go through a pipeline of operations until aggregated

Question 90

how do you use count to find the number of documents in the collection

Answer 90

$count : "name"

Question 91

how do you count a specific attribute in a document in a collection

Answer 91

$match before counting

Question 92

db.createView(viewName, collection, pipeline, options)

Answer 92

temporarily returns a collection that will not be kept in the database

Question 93

$lookup

Answer 93

creates a cross product of two collections based on a common field

Question 94

$unwind

Answer 94

deconstructs/ flattens an array into individual docs