PostgreSQL

Question 1

What is PostgreSQL and what are some alternative relational databases?

Answer 1

• PostgreSQL is a powerful, free, open source Relational Database Management System. (relational databases use some variation of the SQL language… opposite of NoSQL)
• alternatives: mySQL, SQLite, Oracle

Question 2

What are some advantages of learning a relational database?

Answer 2

• they are ubiquitous
• they support good guarantees about data integrity
• they can store and modify data in a way that makes data corruption as unlikely as possible
• developers can set up their database to reject “bad” data and not worry about data being “half written”

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 that defines how the data in a relational database should be organized

Question 5

What is a table in a database?

Answer 5

• a list of rows each having the same set of attributes (columns)
• a sort of spreadsheet where each row is a record in that spreadsheet

Question 6

What are rows and columns in a database?

Answer 6

• -columns are a set of data values of a particular type. they contain the column name, data type, or any other attributes for the column
• rows, aka “tuples”, represent the data item in a table

Question 7

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

Answer 7

-where JavaScript is imperative in that you tell JavaScript what to do, SQL is declarative. you just describe the results you want, and SQL will come up with its own plan for getting those results (like html/css)

Question 8

How do you retrieve specific columns from a database table?

Answer 8

-“select” clause

select “column-name-1”,
“column-name-2”
from “database-table-name”

Question 9

How do you filter rows based on some specific criteria?

Answer 9

-“where” clause

select “xyz-column”
from “xyz-table-name”
where “xyz-column-2” = “abc”

Question 10

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

Answer 10

, =, and !=

Question 11

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

Answer 11

-“limit” clause (comes last)

select *
from “xyz-table-name”
limit 10

Question 12

How do you retrieve all columns from a database table?

Answer 12

select *

Question 13

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

Answer 13

-“order by” clause; asc/desc

Question 14

How do you add a row to a SQL table?

Answer 14

insert into “products” (“name”, “description”, “price”, “category”)
values (‘Ostrich Pillow’, ‘Feel comfy and cozy!’, 99, ‘self care’);

Question 15

What is a tuple?

Answer 15

a list of values (aka a row in a database table)

Question 16

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

Answer 16

specify more than one tuple of values, separated by commas

insert into “products” (“name”, “description”, “price”, “category”)
values (‘Ostrich Pillow’, ‘Feel comfy and cozy!’, 99, ‘self care’),
(‘Tater Mitts’, ‘Scrub some taters!’, 6, ‘cooking’)
returning *;

Question 17

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

Answer 17

“returning” clause

Question 18

How do you update rows in a database table?

Answer 18

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

Question 19

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

Answer 19

-if you don’t include a criteria, then the query will update every row in the table

Question 20

How do you delete rows from a database table?

Answer 20

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

Question 21

How do you accidentally delete all rows from a table?

Answer 21

delete from “table-name”;

no “where” clause

Question 22

What is a foreign key?

Answer 22

a column that specifically refers to values in a column from another table

Question 23

How do you join two SQL tables?

Answer 23

-“join” clause

select “products”.”name” as “product”,
“suppliers”.”name” as “supplier”
from “products”
join “suppliers” using (“supplierId”);

Question 24

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

Answer 24

-use keyword “as”

select “products”.”name” as “product”,
“table2”.”columnName” as “supplier”

Question 25

What are some examples of aggregate functions?

Answer 25

MIN, MAX, AVG, SUM, and COUNT

Question 26

What is the purpose of a group by clause?

Answer 26

used with aggregate functions (min, max, avg, etc) to show one value per grouped field