SQL

Question 1

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

Answer 1

It’s a declarative language you only need to tell it what to do

Question 2

How do you retrieve specific columns from a database table?

Answer 2

by using select “column name”

Question 3

How do you filter rows based on some specific criteria?

Answer 3

by using where + condition

Question 4

What are the benefits of formatting your SQL?

Answer 4

To make it more readable

Question 5

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

Answer 5

< ,> , != , =

Question 6

How do you limit the number of rows returned in a result set?

Answer 6

with limit (must be at the end)

Question 7

How do you retrieve all columns from a database table?

Answer 7

with *

Question 8

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

Answer 8

with order by (in ascending)
else place desc for descending

Question 9

How do you skip lines of code?

Answer 9

With offset

Question 10

How do you add a row to a SQL table?

Answer 10

insert into “table” (“property”, …)
values (‘value’, …)

Question 11

What is a tuple?

Answer 11

A list of values inside ( )

Question 12

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

Answer 12

insert into “table” (“property”, …)
values (‘value’, …),
(‘value’, …)

Question 13

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

Answer 13

insert into “table” (“property”, …)
values (‘value’, …),
(‘value’, …)
return *

Question 14

How do you update rows in a database table?

Answer 14

update “table”
set “target” = value
where “condition” = comparison;

Question 15

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

Answer 15

To pin point the specific target

Question 16

How do you delete rows from a database table?

Answer 16

delete
from “table”
where “column” = value
returning *;

Question 17

How do you accidentally delete all rows from a table?

Answer 17

delete
from “table”;

(you don’t add where)

Question 18

What is a foreign key?

Answer 18

an id/key from another table

Question 19

How do you join two SQL tables?

Answer 19

select *
from “table”
join “table2” using (“tableId”);

Question 20

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

Answer 20

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

Question 21

What are some examples of aggregate functions?

Answer 21

count( )
sum( )
total( )
avg( )
min( )
max( )

Question 22

What is the purpose of a group by clause?

Answer 22

To separate rows from groups