SQL

Question 1

What is PostgreSQL and what are some alternative relational databases?

Answer 1

PostgreSQL is a free open-source relational database management system

Question 2

What are some advantages of learning a relational database?

Answer 2

As a developer it is likely I will be working close to a database, so best to have knowledge of.

Question 3

What is one way to see if PostgreSQL is running?

Answer 3

by running ‘sudo service postgresql status’ command

Question 4

What is a database schema?

Answer 4

A collection of tables in a database.

Question 5

What is a table?

Answer 5

A list of rows and columns that store data in relations.

Question 6

What is a row?

Answer 6

A row is an entry in a table and every row contains the same set of attributes

Question 7

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

Answer 7

SQL is a declarative language like html/css whereas other languages like JavaScript are imperative programing languages.
Declarative languages typically describe the results they want and the program environment gets the result in what ever way the program environment wants. Imperative languages tell an environment what to do and how to do it.

Question 8

How do you retrieve specific columns from a database table?

Answer 8

By using the select keyword follow by one or more column name wrapped in double quotes.

Question 9

How do you filter rows based on some specific criteria?

Answer 9

By using the where clause

Question 10

What are the benefits of formatting your SQL?

Answer 10

For 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

• (asterisk)symbol

Question 14

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

Answer 14

order by (use desc for descending order)

Question 15

How do you add a row to a SQL table?

Answer 15

By using an insert statement

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

A comma separated list of tuples after the values clause

Question 18

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

Answer 18

Use the returning with either an * for all columns or specify with a tuple of desired columns

Question 19

How do you update rows in a database table?

Answer 19

By using an update statement

Question 20

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

Answer 20

Because if you don’t specify with a where clause, every entry in the table will get updated.

Question 21

How do you delete rows from a database table?

Answer 21

By using a delete statement

Question 22

How do you accidentally delete all rows from a table?

Answer 22

By not specifying what to delete with the where clause

Question 23

What is a foreign key?

Answer 23

A foreign key is a column who’s purpose is to reference a column in a different table.

Question 24

How do you join two SQL tables?

Answer 24

Join clause

Question 25

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

Answer 25

By creating an Alias name with the as keyword