NPM/PostgreSQL

Question 1

What is NPM?

Answer 1

world's largest software registry. Node Package Manager.
consists of 3 distinct components:
1. the website
2. the Command Line Interface
3. the registry

Question 2

What is a package?

Answer 2

reusable codes.
a Node Modules or contain Node Modules.
is a file or directory and a package.json file.

Question 3

How can you create a package.json with npm?

Answer 3

npm init –yes

Question 4

What is a dependency and how to you add one to a package?

Answer 4

dependency - the other modules that this module uses. to specify the packages your project depends on.
someone else's code, for the project to run on

You can add dependencies to a package.json file from the command line or by manually editing the package.json file.
from command line: npm install [–save-prod]
manually: add an attribute called ‘dependencies’ that references the name and semantic version of each dependency.

{
  "name": "my_package",
  "version": "1.0.0",
  "dependencies": {
    "my_dep": "^1.0.0",
    "another_dep": "~2.2.0"
  }
}

Question 5

What happens when you add a dependency to a package with npm?

Answer 5

the package is automatically added as a dependency

Question 6

What is PostgreSQL and what are some alternative relational databases?

Answer 6

PostgreSQL is an open source object-relational database system (relational database system).
alternatives are Microsoft SQL Server, MySQL, Oracle Database. maybes = MongoDB, Redis, Neo4j

Question 7

What are some advantages of learning a relational database?

Answer 7

Simple Model. A Relational Database system is the most simple model, as it does not require any complex structuring. Data Accuracy, Easy access to Data. Used very frequently, it’s all shared query language. share the same syntax. compacted very well. good at preventing data duplication. very flexible based on what the data is. Essentially a table

Question 8

What is one way to see if PostgreSQL is running?

Answer 8

on terminal enter the command / having the top command.

sudo service postgresql status

Question 9

What is a database schema?

Answer 9

is a collection of tables. defines the structure of databas.

Question 10

What is a table?

Answer 10

A table is a list of rows each having the same set of attributes. For example, all students in a “students” table could have “firstName”, “lastName”, and “dateOfBirth” attributes. Attributes are commonly referred to as columns

Question 11

What is a row?

Answer 11

is the actual record of single data.

the table it defines what each row should have, each row is the instance of the data.

Question 12

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

Answer 12

is the primary way of interacting with relational databases. way of retrieving, creating, and manipulating data in a relational database.
it differs from JS which is an imperative programming language, whereas SQL is a declarative programming language. => describes the results they want and the programming environment comes up with its own plan for getting the results (like HTML CSS)

Question 13

How do you retrieve specific columns from a database table?

Answer 13

with SELECT keyword
SELECT “attribute” (if more than one ,)
FROM clause “table”

Question 14

How do you filter rows based on some specific criteria?

Answer 14

after FROM clause use WHERE clause “column” = > < != ‘field’

Question 15

What are the benefits of formatting your SQL?

Answer 15

for consistent style and readability

Question 16

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

Answer 16

=, !=, >, <, >= ,<=, < >, BETWEEN

Question 17

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

Answer 17

with LIMIT clause (number without ‘’)

Question 18

How do you retrieve all columns from a database table?

Answer 18

SELECT (keyword with) *

Question 19

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

Answer 19

ORDER BY (clause ) “column” desc. if desc left blank, ascending by default.

Question 20

How do you add a row to a SQL table?

Answer 20

INSERT INTO “name of table” (“column”, column”)
VALUES (‘value’, ‘value’)
(‘value’, ‘value’)
RETURNING *;
in the same order as the columns they belong to

Question 21

What is a tuple?

Answer 21

a list of values. rows. a record stored in a row

Question 22

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

Answer 22

INSERT INTO “name of table” (“column”, column”)
VALUES (‘value’, ‘value’),
(‘value’, ‘value’)
RETURNING *;
in the same order as the columns they belong to

Question 23

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

Answer 23

RETURNING *;

can also specify columns with the RETURNING keyword

Question 24

How do you update rows in a database table?

Answer 24

update “products”
set “price” = 200,
“name” = ‘Super ShakeWeight’,
“description” = ‘Makes you ULTRA strong!’
where “productId” = 24;

Question 25

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

Answer 25

because it will update every row in the table. essentially the whole column.

Question 26

How do you delete rows from a database table?

Answer 26

delete from “products”
where “productId” = 24
returning *;

Question 27

How do you accidentally delete all rows from a table?

Answer 27

when no other keywords were not provided like delete from “products”; will delete the whole table rows

Question 28

What is a foreign key?

Answer 28

a column that specifically refers to values in a column of another table. is a constraint that one column has to match with another column

Question 29

How do you join two SQL tables?

Answer 29

FROM “table-name”

JOIN “table-name” USING (“column”)

Question 30

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

Answer 30

JOIN “table-name” AS “tn” USING (“column”);

Question 31

What are some examples of aggregate functions?

Answer 31

max(), avg(), count(), sum()
more on
https://www.postgresql.org/docs/current/functions-aggregate.html

aggravate bunch of values into one value, it returns one value. similar to join() in JS and reduce()

Question 32

What is the purpose of a group by clause?

Answer 32

The GROUP BY Clause is utilized in SQL with the SELECT statement to organize similar data into groups. It combines the multiple records in single or more columns using some functions.