PostgreSQL/SQL

Question 1

What is PostgreSQL and what are some alternative relational databases?

Answer 1

PostgreSQL is a relational database. It is cited as the most advanced open-source and free relational database available. MySQL, SQL Server by Microsoft, and Oracle are some alternative relational databases.

Question 2

What are some advantages of learning a relational database?

Answer 2

Most developers work with relational databases a little bit and many other relational databases work off the same SQL language.

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. It defines how the data in a relational database should be organized.

Question 5

What is a table?

Answer 5

Data stored in ‘relations’

Question 6

What is a row?

Answer 6

A row is collection of attributes or a single record in a table

Question 7

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

Answer 7

SQL is a declarative language like HTML and CSS whereas JavaScript is an imperative language. With SQL, we describe the results we want and the environment figures out how to provide us with the result

Question 8

How do you retrieve specific columns from a database table?

Answer 8

You use select followed by the column names in double quotes (separated by a comma if multiple)

Question 9

How do you filter rows based on some specific criteria?

Answer 9

You can use where “row” and an assignment operator like =, <, >, or != and the value. If the value is a string use single quotes

Question 10

What are the benefits of formatting your SQL?

Answer 10

It is more consistent and easier to read/understand

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

Use the limit keyword and the maximum number of rows you want returned

Question 13

How do you retrieve all columns from a database table?

Answer 13

You can use the universal selector (*) after the select keyword
e.g. select *

Question 14

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

Answer 14

A result set returns in ascending order by default. If you want it to be returned in descending order you would use the order by keywords, the column name in double quotes, followed by the desc keyword
e.g. order by “price” desc

Question 15

How do you add a row to a SQL table?

Answer 15

insert into

Question 16

What is a tuple?

Answer 16

A list of values being added to a SQL table

Question 17

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

Answer 17

You separate each set of values with a ,

- Recommended to put on new lines for clarity

Question 18

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

Answer 18

Use a returning statement

Question 19

How do you update rows in a database table?

Answer 19

With the update from keywords

Question 20

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

Answer 20

If you do not then it will update all of the items in a table

Question 21

How do you delete rows from a database table?

Answer 21

With the delete from keywords

Question 22

How do you accidentally delete all rows from a table?

Answer 22

Similar to update from, if you do not specify where then you can run into the issue of deleting everything

Question 23

What is a foreign key?

Answer 23

The shared data value between tables

Question 24

How do you join two SQL tables?

Answer 24

You first select the items you want to use from each table
Select which table you want as the base with from
Then using the join keyword and using keyword followed by the foreign key in parenthesis (can also have more items separated by a comma))

Question 25

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

Answer 25

You can alias them using the as keyword

Question 26

What are some examples of aggregate functions?

Answer 26

Max, min, sum, count

Question 27

What is the purpose of a group by clause?

Answer 27

To separate groups by rows so that we can perform aggregate functions on them