SQL

Question 1

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

Answer 1

SQL (Structured Query Language) is the primary way of interacting with relational databases.

SQL is a declarative programming language.

Question 2

How do you retrieve specific columns from a database table?

Answer 2

A Select statement

select “name”, “price”
from “products”;

Question 3

How do you filter rows based on some specific criteria?

Answer 3

where “column name” = ‘attribute name’;

Question 4

What are the benefits of formatting your SQL?

Answer 4

It makes it look cleaner.

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

limit

Question 7

How do you retrieve all columns from a database table?

Answer 7

select *

from “column”;

Question 8

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

Answer 8

desc keyword

Question 9

How do you add a row to a SQL table?

Answer 9

Use the insert statement

Question 10

What is a tuple?

Answer 10

A finite ordered list of elements

SQL: A set of sets, defining a container with order.

Question 11

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

Answer 11

specify more than one tuple of values separated by commas.

data, data, data),
(data, data, data

Question 12

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

Answer 12

Use the returning clause. If you want all columns you can use * otherwise use a comma-separated list instead.

Question 13

How do you update rows in a database table?

Answer 13

update

Question 14

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

Answer 14

If you don’t specify a specific row it will update all items in that column.

Question 15

How do you delete rows from a database table?

Answer 15

delete from “table”
where “row” = ‘value’

Complex where/and:
where “row” = ‘value’
and “row” (, =, !=) ‘value’;

Question 16

How do you accidentally delete all rows from a table?

Answer 16

delete from “table”;

Question 17

What is a foreign key?

Answer 17

When a columns data references another tables data.

Question 18

How do you join two SQL tables?

Answer 18

select “column”
from “table”
join “table” using (“column”)

Question 19

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

Answer 19

Aliasing

select “table”.”column” as “newLabel”

this can also be done when using from and join.
select “table”.”column” as “newLabel”
from “products” as “p”
join “suppliers” as “s” using (“supplierId”); (for example)

repeat as necessary by separating with commas.

Question 20

What are some examples of aggregate functions?

Answer 20

max(): Finds max number
avg(): Finds average
count(*): Counts number of rows
min()
sum()
every()
look into JSON aggregate functions

Question 21

What is the purpose of a group by clause?

Answer 21

Separates rows into groups to perform aggregate functions.