Databases

Question 1

What is PostgreSQL and what are some alternative relational databases?

Answer 1

open-source relational database system; some others are MySQL, SQL Server, and Oracle

Question 2

What are some advantages of learning a relational database?

Answer 2

good for modeling and storing related data; also supports good guarantees about data integrity

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 relational database that defines how the data should be organized

Question 5

What is a table?

Answer 5

a list of rows each having the same set of attributes

Question 6

What is a row?

Answer 6

a record in the database

Question 7

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

Answer 7

SQL is a declarative programming language, while JavaScript is an imperative programming language

Question 8

How do you retrieve specific columns from a database table?

Answer 8

select clause indicating column names

Question 9

How do you filter rows based on some specific criteria?

Answer 9

where clause

Question 10

What are the benefits of formatting your SQL?

Answer 10

consistent style and readability

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

limit clause

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

Question 15

How do you add a row to a SQL table?

Answer 15

insert into “tableName” (“columnNames”)

values (‘values’)

Question 16

What is a tuple?

Answer 16

a list of values

Question 17

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

Answer 17

insert into … values… - specify each tuple of values in parentheses, separated by commas

Question 18

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

Answer 18

returning * (or columnNames) - add to the end of the insert into statement

Question 19

How do you update rows in a database table?

Answer 19

update “tableName”, set “columnName” = value

Question 20

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

Answer 20

to target the specific rows you want to update

Question 21

How do you delete rows from a database table?

Answer 21

delete from “tableName” where “columnName” = ‘value’

Question 22

How do you accidentally delete all rows from a table?

Answer 22

if you don’t include the where clause to specify the rows you want to delete

Question 23

What is a foreign key?

Answer 23

a column in one table that references a value in another table

Question 24

How do you join two SQL tables?

Answer 24

join “otherTable” using (“foreignKey”)

Question 25

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

Answer 25

use as to specify the alias

Question 26

What are some examples of aggregate functions?

Answer 26

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

Question 27

What is the purpose of a group by clause?

Answer 27

allows you to separate rows into groups and perform aggregate functions on those groups of rows