postgreSQL

Question 1

What is PostgreSQL and what are some alternative relational databases?

Answer 1

PostgreSQL is a relational database. Often cited as the most advances open source database of its kind. Other relational databases are MySQL, SQL, and Oracle

Question 2

What are some advantages of learning a relational database?

Answer 2

Relational databases work around the SQL language so there’s a level of standardization. If you’re storing related data, it’s probably best to use a relational database. They also make data corruption as unlikely as possible.

Question 3

What is one way to see if PostgreSQL is running?

Answer 3

You can check the top command to see if a PostgreSQL process is running, you can run a Postgres status command, or you can go to your database address and check as well

Question 4

What is a database schema?

Answer 4

A database schema is a collection of tables A schema defines how the data in a relational database should be organized. Is defined up front

Question 5

What is a table?

Answer 5

In terms of a relational database, tables are relations and contain a list of rows

Question 6

What is a row?

Answer 6

A row is a section of a table and each row has the same set of attributes. Each row can be thought of as a record.

Question 7

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

Answer 7

SQL is the language used to interact with relational databases. It’s different from JS in that it’s a declarative language. Where programmers describe the results they want as opposed to imperative programming languages where you tell the program what to do and how to do it.

Question 8

How do you retrieve specific columns from a database table?

Answer 8

you use the SELECT command and specify which column you want and then use the FROM keyword to specify which table it’s from

Question 9

How do you filter rows based on some specific criteria?

Answer 9

you use the WHERE clause and it needs to have an expression that evaluates to a boolean

Question 10

What are the benefits of formatting your SQL?

Answer 10

readability

Question 11

What are four comparison operators than 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

you use the LIMIT keyword after your selection parameters… followed by the number of rows you want returned

Question 13

How do you retrieve all columns from a database table?

Answer 13

with the * symbol

Question 14

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

Answer 14

with the ORDER BY clause

Question 15

How do you add a row to a SQL table?

Answer 15

The statement begins with the insert keyword

The table to insert into is specified in “ double quotes

The list of columns being inserted is wrapped in () parenthesis

The values being inserted are also wrapped in () in parenthesis in the same order as the columns they belong to… In SQL, a list of values is referred to as a tuple

Text values are wrapped in ‘ single quotes

Numeric values are represented with literal numbers (or decimals if applicable)

Question 16

What is a tuple?

Answer 16

a list of real values

Question 17

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

Answer 17

By including as many tuples as you want rows

Question 18

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

Answer 18

returning * clause

Question 19

How do you update rows in a database table?

Answer 19

update “products”

set “price” = 100;

Question 20

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

Answer 20

without a where clause, all values will be updated

Question 21

How do you delete rows from a database table?

Answer 21

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

Question 22

How do you accidentally delete all rows from a table?

Answer 22

by not including a where clause

Question 23

What is a foreign key?

Answer 23

a foreign key is a key that is shared by 2 or more tables

Question 24

How do you join two SQL tables?

Answer 24

select statement followed by the specific columns you want from each table
from clause from the parent table
join the second table using the foreign key that they have in common

Question 25

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

Answer 25

you use the “as” clause to give it a temporary name… this is called aliasing

Question 26

What are some examples of aggregate functions?

Answer 26

sum, avg, count(*)

Question 27

What is the purpose of a group by clause?

Answer 27

The purpose of a “group by” clause is to perform aggregate functions on only a certain group of rows.