SQL

Question 1

What is PostgreSQL and what are some alternative relational databases?

Answer 1

PostgreSQL is a relational database management system written using a variation of SQL; other examples of relational databases include MySQL, SQL Server, and Oracle

Question 2

What are some advantages of learning a relational database?

Answer 2

It is used everywhere and is generally better at modeling data

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 in a database; a formal description of how the data should be organized

Question 5

What is a table?

Answer 5

A collection of rows in a database that all share the same columns(attributes)

Question 6

What is a row?

Answer 6

An instance of data containing columns(attributes)

Question 7

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

Answer 7

SQL stands for Structured Query Language and is the primary way of interacting with relational databases; it is a declarative language (e.g. HTML and CSS) where the programmer uses pre-built keywords to describe the desired result, as opposed to a imperative language (e.g. JavaScript) where the programmer tells the program what to do and how to do it

Question 8

How do you retrieve specific columns from a database table?

Answer 8

select “column”,
“column”,
…
from “table”

Question 9

How do you filter rows based on some specific criteria?

Answer 9

where “attribute” = criteria

Question 10

What are the benefits of formatting your SQL?

Answer 10

It makes it easier to read

Question 11

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

Answer 11

=, !=, >, ‘less than sign’

Question 12

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

Answer 12

limit number

Question 13

How do you retrieve all columns from a database table?

Answer 13

select *

Question 14

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

Answer 14

order by “attribute” [desc]

Question 15

How do you add a row to a SQL table?

Answer 15

insert into “table” (“attribute1”, “attribute2”, …)

values (“value1”, “value2”, …)

Question 16

What is a tuple?

Answer 16

A list of values enclosed in parentheses

Question 17

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

Answer 17

separate the tuples with commas

Question 18

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

Answer 18

returning *

Question 19

How do you update rows in a database table?

Answer 19

update “table”
set “attribute” = newValue
where “attribute” = criteria

Question 20

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

Answer 20

Otherwise, SQL will update every row in the table

Question 21

How do you delete rows from a database table?

Answer 21

delete from “table”

where “attribute” = criteria

Question 22

How do you accidentally delete all rows from a table?

Answer 22

You exclude the where clause

Question 23

What is a foreign key?

Answer 23

A column in a table that is used in another table, which allows the tables to be joined

Question 24

How do you join two SQL tables?

Answer 24

from “firstTable”

join “secondTable” using (“foreignKey”)

Question 25

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

Answer 25

“originalName” as “newName”

Question 26

What are some examples of aggregate functions?

Answer 26

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

Question 27

What is the purpose of a group by clause?

Answer 27

It specifies the data on which to apply the aggregate functions