08 - Limit + Aliasing in MySQL

08-Limit + Aliasing in MySQL

https://youtu.be/ZnAydTqCtFU?si=z_qUXNIqoEizJn4-

TOTAL: 3.56 MINS

-- LIMIT and ALIASING

-- Limit is just going to specify how many rows you want in the output

SELECT *

FROM employee_demographics

LIMIT 3;

-- if we change something like the order or use a group by it would change the output

SELECT *

FROM employee_demographics

ORDER BY first_name

LIMIT 3;

-- now there is an additional paramater in limit which we can access using a comma that specifies the starting place

-- DẤU PHẨY là xác định ĐIỂM BẮT ĐẦU LIMIT

SELECT *

FROM employee_demographics

ORDER BY first_name;

SELECT *

FROM employee_demographics

ORDER BY first_name

LIMIT 3,2;

-- this now says start at position 3 and take 2 rows after that

-- this is not used a lot in my opinion

-- you could us it if you wanted to select the third oldest person by doing this:

SELECT *

FROM employee_demographics

ORDER BY age desc;

-- we can see it's Donna - let's try to select her

SELECT *

FROM employee_demographics

ORDER BY age desc

LIMIT 2,1;

01:43

-- ALIASING

-- aliasing is just a way to change the name of the column (for the most part)

-- it can also be used in joins, but we will look at that in the intermediate series

SELECT gender, AVG(age)

FROM employee_demographics

GROUP BY gender

;

-- we can use the keyword AS to specify we are using an Alias

SELECT gender, AVG(age) AS Avg_age

FROM employee_demographics

GROUP BY gender

;

-- although we don't actually need it, but it's more explicit which I usually like

SELECT gender, AVG(age) Avg_age

FROM employee_demographics

GROUP BY gender

;