PostgreSQL & SQL

Question 1

What is PostgreSQL and what are some alternative relational databases?

Answer 1

Relational Database Management System (RDBMS).

MySQL, SQL Server by Microsoft, and Oracle by Oracle Corporation.

Question 2

What are some advantages of learning a relational database?

Answer 2

Good for storing related data.

They support good guarantees about data integrity. They can store and modify data in a way that makes data corruption as unlikely as possible. This means that 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; defines how the data in a relational database should be organized

Question 5

What is a table?

Answer 5

Stored data in relations; a list of rows each having the same set of attributes; Attributes are commonly referred to as columns.

sort of spreadsheet

Question 6

What is a row?

Answer 6

Data entries with the same set of attributes.

Question 7

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

Answer 7

Structured Query Language (SQL); primary way of interacting with relational databases. It is a powerful way of retrieving, creating, and manipulating data in a relational database;

SQL is a declarative programming language, programmers describe the results they want and the programming environment comes up with its own plan for getting those results.

Question 8

How do you retrieve specific columns from a database table?

Answer 8

select “column-name”,
“column-name”
from “table-name”;

Question 9

How do you filter rows based on some specific criteria?

Answer 9

where “column-name” = ‘column-value’;

string using single quotes ‘column-value’; number just use number

Question 10

What are the benefits of formatting your SQL?

Answer 10

for consistent style and therefore readability.

Question 11

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

Answer 11

!=, =, ‘>’, ‘less-than’

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 “price” desc

Question 15

How do you add a row to a SQL table?

Answer 15

insert into “table-name” (“column-name”)

Question 16

What is a tuple?

Answer 16

a list of values in SQL

Question 17

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

Answer 17

insert into “table-name” (“column1”, “column2”,
“column3”, “column4”)
values (‘value1, ‘value2’, 99, ‘value4’);

Question 18

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

Answer 18

returning *

returning ‘column-name1’, ‘column-name2’

Question 19

How do you update rows in a database table?

Answer 19

update “table-name”
set “column-name” = new-value
[where “column-name” = column-value;]

Question 20

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

Answer 20

Without ‘where’, you will update all entries in the table.

Question 21

How do you delete rows from a database table?

Answer 21

delete from “table-name”
where “column-name” = column-value
[returning *];

delete from “table-name”
where “column-name1” = ‘column-value’
and “column-name2” < column-value

Question 22

How do you accidentally delete all rows from a table?

Answer 22

delete from “table-name”;

leaving out the ‘where’ statement

Question 23

What is a foreign key?

Answer 23

a column that links 2 different tables (same column names in 2 different tables)

Question 24

How do you join two SQL tables?

Answer 24

select *
from “table-name1”
join “table-name2” using (“foreign-key”);

select “table-name1”.”column-name1”,
“table-name2”.”column-name2”
from “table-name1”
join “table-name2” using (“foreign-key”);

Question 25

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

Answer 25

columns:

select “table1”.”column” as “alias1”,
“table2”.”column” as “alias2”
from “table1”
join “table2” using (“foreign-key”);

tables:

select "p"."name" as "product",
       "p"."category",
       "s"."name" as "supplier",
       "s"."state"
  from "products" as "p"
  join "suppliers" as "s" using ("supplierId");

Question 26

What are some examples of aggregate functions?

Answer 26

max(), avg(), count(), min(), sum(), and every(), etc.

Question 27

What is the purpose of a ‘group by’ clause?

Answer 27

To separate rows into groups and perform aggregate functions on those groups of rows.