[Udemy] 15 Days of SQL - Day 1: ORDER BY, SELECT, LIMIT, COUNT

ORDER BY

• ORDER BY 'COLUMN' 
• ASC - default, DESC
• using index number instead of column names

SELECT DISTINCT

• Eliminate duplicated values
• more than two columns - considering all columns and show only unique values
• Find out unique values in columns

*Challenge

1. show different prices that have been paid
2. order the prices from high to low

 

LIMIT

• Used to limit the number of rows in the output
• Always at the very end of your query
• Can help to get a quick idea about a table

• 

 

COUNT

• Count the number of rows in a output
• Used often in combination with grouping & filtering
• Nulls will not be counted

  

• Use with DISTINCT - count only unique values

• 

Day 1 Challenge

1) Create a list of all the distinct districts customers are from.

SELECT DISTINCT district
FROM address

 

2) What is the latest rental date?

SELECT rental_date
FROM rental
ORDER BY rental_date DESC
LIMIT 1

 

3) How many films does the company have?

SELECT 
COUNT(*)
FROM film

4) How many distinct last names of the cutomers are there?

SELECT 
COUNT(DISTINCT last_name)
FROM customer