Week 9

Question 1

What is PostgreSQL and what are some alternative relational databases?

Answer 1

PostgreSQL is a relational database system
Alternatives: MySQL, SQL Server by Microsoft, Oracle by Oracle Corporation

Question 2

What are some advantages of learning a relational database?

Answer 2

It’s the most widely used kind of data base so the chances that you’ll run into it as a developer is high
It also can store and modify data in a way that makes data corruption as unlikely as possible

Question 3

What is one way to see if PostgreSQL is running?

Answer 3

sudo service postgresql status

Question 4

What is a database schema?

Answer 4

a collection of tables
describes the rules of how tables can be stored
it defines how the data in a relational database should be organized

Question 5

What is a table?

Answer 5

a list of rows, each having the same set of attributes aka columns
ex: all students in a “students” table could have “firstName”, “lastName”, and “dateofBirth” attributes

Question 6

What is a row?

Answer 6

A collection of attributes for a single record in the table
a record/single instance of data

Question 7

What is SQL and how is it different from languages like JS?

Answer 7

SQL is a declarative language - aka you describe the results you want and the program comes up with its own plan for getting the results
JS is an imperative language – you tell js what to do and how to do it

Question 8

How do you retrieve specific columns from a database table?

Answer 8

select “name of column” from “name of table”

Question 9

How do you filter rows based on some specific criteria?

Answer 9

use “where” and the criteria

Question 10

What are the benefits of formatting your SQL?

Answer 10

consistency and readability

Question 11

What are four comparison operators that can be used in a where clause?

Answer 11

=, <, >, !=

Question 12

How do you limit the number of rows returned in a result set?

Answer 12

limit with an integer

Question 13

How do you retrieve all columns from a database table?

Answer 13

use * (asterisk)

Question 14

How do you control the sort order of a result set?

Answer 14

you specify it with order by “column-name” … default is ascending order

Question 15

How do you add a row to a SQL table?

Answer 15

insert into “tableName” (“col1”, “col2”, …)
values (‘val1’, ‘val2’, …)

column names are wrapped in “ “
values are wrapped in ‘ ‘

Question 16

What is a tuple?

Answer 16

A list of values inside of parenthesis with each value wrapped in ‘ ‘

Question 17

How do you add multiple rows to a SQL table at once?

Answer 17

You separate the tuples by commas

Question 18

How do you get back the row being inserted into a table without a separate select statement?

Answer 18

use returning

• for all columns or comma-separated list of column names if you want specific ones

Question 19

How do you update rows in a database table?

Answer 19

update “tableName”
set “column” = ‘value’
where “column” = ‘value’

ex:
update “products”
set “price” = 100
where “productId” = 24

Question 20

Why is it important to include a where clause in your update statements?

Answer 20

If you don’t, it’ll update every row in the table

Question 21

How do you delete rows from a database table?

Answer 21

delete from “table”
where “column” = ‘value”

Question 22

How do you accidentally delete all rows from a table?

Answer 22

delete from “tableName”
aka forget a where clause

Question 23

What is a foreign key?

Answer 23

A set of attributes (or columns) that refers to the primary key of another table

Question 24

How do you join two SQL tables?

Answer 24

select keyword followed by attributes
from keyword followed by name of first table
join keyword followed by name of second table with the using keyword followed by the foreign key in quotes and parentheses
ex:
select *
from “products”
join “suppliers” using (“supplierId”)

Question 25

How do you temporarily rename columns or tables in a SQL statement?

Answer 25

Dot notation –> table name in quotes followed by dot and column name in quotes (if you’re renaming column” followed by as keyword followed by the temp name for the column in quotes
ex:
“Products”.”name” as “product”
or
“Products” as “p”

Question 26

What are some examples of aggregate functions?

Answer 26

max(), avg(), count(), min(), sum(), every()

Question 27

What is the purpose of a group by clause?

Answer 27

places rows into groups/categories
allows you to use aggregates on those groups instead of each row individually

Question 28

What are the three states a Promise can be in?

Answer 28

1. Pending: initial state, neither fulfilled nor rejected
2. Fulfilled: operation was completed successfully
3. Rejected: operation failed (error)

Question 29

How do you handle the fulfillment of a Promise?

Answer 29

then() method

Question 30

How do you handle the rejection of a Promise?

Answer 30

catch() method
OR
use the 2nd parameter in the then() method

Question 31

What is webpack?

Answer 31

a tool that lets you bundle your javascript modules
starts from multiple modules and the end result is “fewer files” which is commonly 1 file referred to as a bundle

Question 32

How do you add a devDependency to a package?

Answer 32

nmp install <package_name> --save-dev</package_name>

Question 33

What is an npm script?

Answer 33

npm scripts are terminal commands that perform a set of actions/allows you to execute repetitive tasks
essentially a command line but with a nickname

Question 34

How do you execute webpack with npm run?

Answer 34

use npm run along with the name that you assigned to the webpack in the script

Question 35

What is syntactic sugar?

Answer 35

Syntax within a language that is designed to make things easier to read or to express

Question 36

What is the typeof an ES6 class?

Answer 36

function

Question 37

Describe ES6 syntax

Answer 37

class keyword followed by option name and curly braces
inside of curly braces are properties and prototype methods that you want inside of the object
ex:
class Student {
constructor(firstName, lastName, subject) {
this.firstName = firstName;
this.lastName = lastName;
this.subject = subject;
}

getFullName() {
const { firstName, lastName } = this;
return ${firstName} ${lastName};
}

getIntroduction() {
const { subject } = this;
const fullName = this.getFullName();
return Hello, my name is ${fullName} and I am studying ${subject}.;
}
}

Question 38

What is refactoring?

Answer 38

the process of updating existing code to improve design/structure/implementation of software while keeping the functionality

Question 39

How are ES modules different from CommonJS modules?

Answer 39

ES modules are official whereas commonJS are a community effort (browsers do not support common js -> must use tools like webpack to make them work)
ES modules use import/export while commonjs modules use require() / module.exports

Question 40

What kind of modules can webpack support?

Answer 40

commonjs, es and amd modules

Question 41

What is react?

Answer 41

a javascript library for building user interfaces

Question 42

What is a react element?

Answer 42

plain old JS object –> object representation of a virtual DOM node
immutable, has no methods and nothing on the prototype

Question 43

How do you mount a react element to the DOM?

Answer 43

render() which is a method of the reactDom object

Question 44

What is Babel?

Answer 44

JS compiler
a toolchain that is used to convert ES6 code into a backwards compatible version of JS in current and older browsers

Question 45

What is a plug-in?

Answer 45

a customization that you add to an existing piece of software
**adds a specific feature to an existing computer program

Question 46

What is a webpack loader?

Answer 46

loaders are transformations that are applied to the source of a module

Question 47

How can you make babel and webpack work together?

Answer 47

install babel loader

Question 48

What is jsx?

Answer 48

Syntax extension to JS

Question 49

Why must the react object be imported when authorizing JSX in a module?

Answer 49

because jsx is syntactic sugar for the react.createElement() function