MySQL for business developer - Titouan BENOIT

MySQL for business developer Titouan BENOIT – CTO at Welp.fr [email protected]

MySQL for business developer– Titouan BENOIT

Titouan BENOIT – CTO at Welp – [email protected]

– [email protected]

MySQL for business developer - v1.0 2

Titouan BENOIT

mailto:[email protected]

mailto:[email protected]

Plan



1. Introduction

2. Query Language

3. Basics

– SELECT – WHERE – ORDER BY – DISTINCT – LIMIT & OFFSET 4. Advanced

– JOIN – Sub-queries – Math functions – COUNT, SUM, AVG 5. phpMyAdmin

6. Examples/Exercices

MYSQL FOR BUSINESS DEVELOPER

1. Introduction

4

MySQL is an Open Source Relational Database Management System

(RDBMS) – SQL (Structured Query Language) databases

– The second most used in the world

– Main purpose: storing data

In this presentation you will learn to: – Make basics queries to search data into MySQL databases

– Extract data from MySQL databases

– Use PHPMyAdmin

– Compute statistics on data (count, average, …)

1. Introduction



1. Introduction: structure



MySQL Server

Databases

Welp OHA …

Tables

needs

propositions

users

…

id title author_id …

1 Mon titre1 5 …

2 Mon titre2 84 …

3 Mon titre3 6 …

… … … …

data

Columns

Rows


2. Query Language

7

SQL (Structured Query Language)

With SQL we can: – Insert data

– Make queries (select data)

– Update data

– Delete data

– Create and modify schema (tables)

– Manage data access control

2. Query Language




3. Basics

9

SELECT * FROM database.table; – Select all colums from table in the database

– Tips:

• USE database;

SELECT * FROM table

SELECT column1, column2, … FROM table

Alias: SELECT user.email FROM fos_user AS user

Example: – SELECT id, email, first_name, last_name FROM welp_db.fos_user

3. Basics: SELECT



SELECT * FROM table WHERE condition; – Select all colums from table in the database where condition is true

SELECT first_name, evaluation_average FROM fos_user WHERE evaluation_average = 5

– Select users where their average is equal to 5

Comparison operators Logical Operators

3. Basics: WHERE



Operator Description

= equal

< less than

<= less than or equal to

> greater than

>= greater than or equal to

<> or != different, not equal

<=> Equal (also to NULL value)

Operator Symbol Description

AND && AND

OR || OR

XOR Exclusive OR

NOT ! NOT

Example:

SELECT * FROM table ORDER BY column1; – Select all colums from table and order by column1 descending order (default behavior)

SELECT * FROM table ORDER BY column1 DESC; – Descending order

SELECT * FROM table ORDER BY column1 ASC; – Ascending order

SELECT * FROM table ORDER BY column1, column2, …; – Multicolumn order

– Note: the order of column after ORDER BY statement is important. The order will be done on the column1 and then column2, …

3. Basics: ORDER BY



SELECT DISTINCT column FROM table; – Return only different rows (one by ‘column’ occurrences)

Example: – SELECT DISTINCT species FROM animal;

– If I have 300 dogs, 400 cats and 250 elephants, this query will return:

• Dog

• Cat

• Elephant

– SELECT DISTINCT first_name FROM fos_user ORDER BY first_name ASC

3. Basics: DISTINCT



SELECT * FROM table LIMIT 0,10; – Return 10 rows from the beginning (row number 0).

– How to use limit: LIMIT [offset, ]number_of_lines

– Note: the LIMIT statement must be at the end

Other syntaxe: – LIMIT number_of_lines [OFFSET offset];

Examples

3. Basics: LIMIT & OFFSET




4. Advanced

15

INNER JOIN – SELECT need.title, need.category_id, category.id, category.name FROM need

INNER JOIN category ON need.category_id = category.id

ORDER BY need.created_at

LIMIT 10;

– Note: inner join does not select rows where the relation is null (here where need has no category for example)

4. Advanced: JOIN



Need table Category table

need category

INNER JOIN

LEFT JOIN – SELECT user.first_name, media.id AS mediaID, media.name AS avatar

FROM fos_user AS user

LEFT JOIN media ON user.avatar_id = media.id

ORDER BY user.created_at DESC

LIMIT 10, 10

4. Advanced: JOIN



User table Media table

media

LEFT JOIN

RIGHT JOIN – SELECT category.id as categoryID, category.name AS categoryName, event.id AS eventID, event.title AS eventTitle

FROM event

RIGHT JOIN category ON event.category_id = category.id

4. Advanced: JOIN



Category table Event table

Difference with LEFT JOIN This category has no event

This event has no category

RIGHT JOIN LEFT JOIN

Sub-queries – In FROM statement:

• SELECT goodEvaluation.comment, goodEvaluation.evaluation, goodEvaluation.evaluator_id

FROM (

SELECT *

FROM evaluation

WHERE evaluation.evaluation = 5

) as goodEvaluation

WHERE goodEvaluation.evaluator_id = 19

– In WHERE clause:

• SELECT id, title, category_id

FROM need

WHERE category_id IN (

SELECT id

FROM category

WHERE name IN ('Actions à plusieurs', 'Visites de courtoisie')

);

4. Advanced: sub-queries



The sub-query:

Math functions – CEIL(n) or CEILING(n): Return the smallest integer value not less than the argument

– FLOOR(n): Return the largest integer value not greater than the argument

– ROUND(n, d): Round the argument (d number of decimal)

– TRUNCATE(n, d): truncate the argument (d number of decimal)

– POW(n, e) or POWER(n, e): n^e

– SQRT(n): square root of the argument

– MOD(n, div): modulo of the division n/div

– RAND(): return a random value between 0 and 1

– SIGN(): return -1 for 0 and negative values and 1 for positive value

– ABS(): absolute value

– PI()

– COS()

– SIN()

4. Advanced: Math functions



Aggregate functions: – COUNT(), SUM(), AVG(), MAX(), MIN()

SELECT COUNT(*) as nbNeed FROM need WHERE need.category_id = 1

SELECT AVG(fos_user.evaluation_average) as avgEvaluation FROM fos_user

GROUP BY & HAVING – SELECT u.id, u.first_name, COUNT(n.author_id) need_count

FROM fos_user u

LEFT JOIN need n ON n.author_id = u.id

GROUP BY u.id

HAVING need_count > 0

ORDER BY need_count DESC

4. Advanced: COUNT, SUM, AVG




5. phpMyAdmin

22

Databases

5. phpMyAdmin



Tables

5. phpMyAdmin



Table structure

5. phpMyAdmin



Browse data

5. phpMyAdmin



SQL query

5. phpMyAdmin



Export data

5. phpMyAdmin





29

Requirements: – Connect to Welp phpMyAdmin

– Login to prod with the read only user

1 slide with the problem at stake and the next slide the query

Good luck & have fun!




1°/ Retrieve the id, title and the

category_id of the 10 last created_at need




1°/ SOLUTION

SELECT id, title, category_id, created_at FROM need

ORDER BY created_at DESC LIMIT 10




2°/ Retrieve the id, first_name and the rank of fos_user

which has a rank more than or equal to 2 and less than 5

and sort by rank (descending)




2°/ SOLUTION

SELECT id, first_name, rank

FROM fos_user

WHERE rank >= 2 AND rank < 5

ORDER BY rank DESC




3°/ Retrieve all the distinct place_locality as city of the

need and sort them by alphabetical order




3°/ SOLUTION

SELECT DISTINCT(place_locality) as city

FROM need

ORDER BY city ASC




4°/ Retrieve the 12 last created need with their category.

Display the need id, title and the category id and name.




4°/ SOLUTION

SELECT need.id as needID, need.title as needTitle, need.category_id, category.id as

categoryID, category.name as categoryName

FROM need

INNER JOIN category ON need.category_id = category.id

ORDER BY need.created_at DESC

LIMIT 12




5°/ Retrieve fos_user id, first_name, last_name and for

each user display their number of welpActions.

Hint: use GROUP BY user.id




5°/ SOLUTION

SELECT user.id, user.first_name, user.last_name,

COUNT(welp_action.user_id) as WelpActions

FROM fos_user as user

LEFT JOIN welp_action ON user.id = welp_action.user_id

GROUP BY user.id

ORDER BY WelpActions DESC





MySQL for business developer – https://en.wikipedia.org/wiki/MySQL

– https://en.wikipedia.org/wiki/SQL

– http://dev.mysql.com/

– https://openclassrooms.com/courses/administrez-vos-bases-de-donnees-avec-mysql

– http://dev.mysql.com/doc/refman/5.7/en/logical-operators.html

– http://dev.mysql.com/doc/refman/5.7/en/comparison-operators.html

– http://dev.mysql.com/doc/refman/5.7/en/join.html

– https://dev.mysql.com/doc/refman/5.0/en/group-by-handling.html

– http://dev.mysql.com/doc/refman/5.7/en/subqueries.html

– http://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html


SOURCES

https://en.wikipedia.org/wiki/MySQL

https://en.wikipedia.org/wiki/MySQL

https://en.wikipedia.org/wiki/SQL

https://en.wikipedia.org/wiki/SQL

http://dev.mysql.com/

http://dev.mysql.com/

https://openclassrooms.com/courses/administrez-vos-bases-de-donnees-avec-mysql














http://dev.mysql.com/doc/refman/5.7/en/logical-operators.html




http://dev.mysql.com/doc/refman/5.7/en/comparison-operators.html




http://dev.mysql.com/doc/refman/5.7/en/join.html

http://dev.mysql.com/doc/refman/5.7/en/join.html

https://dev.mysql.com/doc/refman/5.0/en/group-by-handling.html






http://dev.mysql.com/doc/refman/5.7/en/subqueries.html

http://dev.mysql.com/doc/refman/5.7/en/subqueries.html

http://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html




MySQL for business developer - Titouan BENOIT

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