MySQL Notes

SQL is a declarative langauage.

MySQL is relational database that describes data and the relationship between data entities.

A database is used for organize/manipulate data and for persistent data.

Database Design

Database organizes data into rows and column. Each row is also call a record.

The goal of database design is to eliminate data redundancy and ensure data integrity and accuracy

Database is made of many independent tables with different purposes. In relational database design, the most important thing is to identify the relationship between the tables.

one-to-one
one-to-many
many-to-many

Primary key: unique identifier of the row of record in the table

Foreign key: value in the table that reference to another record in another table.

There will be time you need to

creating more column,

split large table into smaller one,

creating new table for option data, 1to1 relationship type.

Normalization uses primary and foriegn key to create relationship between tables.
i.e. first normal form, second normal form, third normal form, hight normal form

Basic Query

Creat User

Creating new user and grant full permission

CREATE USER 'newuser'@'localhost' IDENTIFIED BY 'password';

GRANT ALL PRIVILEGES ON * . * TO 'newuser'@'localhost';
FLUSH PRIVILEGES;

CREATE Clause

Creating new table

CREATE TABLE [IF NOT EXIST] my_table_name(
	colume1 unsigned AUTO_INCREMENT PRIMARY KEY,
	colune2 INT 
	colume3 VARCHAR(30),
	colume4 VARCHAR(50) NOT NULL
	.....
)

SELECT Clause

Retrieve row/s from table

SELECT <column name>, <colume name> FROM <table name>;

SELECT type, maker FROM cars;

Will return two columns

SELECT 'hello', 'github'

SELECT * FROM <table_name> This is an example of bad query because it selects everything from the table, which increase disk I/O Best practices is to be explicit in the query.

FROM Clause

Specifying the table or constrain the query result

SELECT type, maker FROM cars;

INSERT Clause

Add row/s into tables

INSERT INTO cars (maker, color)
VALUE('Tesla', 'black');

UPDATE Clause

Modify row/s in table

UPDATE cars SET maker = 'Honda' WHERE id = 1;

DELETE Clause

Remove row/s from table

DELETE FROM cars contacts where id = 2;

Using alias to distinguish column and their association with table. Important when using join query
SELECT c.maker, c.color, b.maker FROM cars c, bicycle b;
Commenting in MySQL workbench with '--'
-- SELECT ........ FROM ........

Distinct qualifier

Remove duplicate, only display uniques data

SELECT DISTINCT c.maker, c.color FROM cars c;

WHERE CLAUSE

Constrains the the query result set; can use boolean expression

(<, >, =, <=, >=,)

SELECT c.owner
FROM car c
WHERE c.maker = 'Tesla';

Combining boolean expression (AND, OR)

SELECT c.owner
FROM car c
WHERE c.maker = 'Tesla' 
AND c.licenseplate = 'ABCDE';

Other operator include BETWEEN, LIKE, IN, IS, IS NOT

ORDER BY

SELECT c.owner, c.maker
FROM car c
ORDER BY c.owner;

Set Function

Compute new value from column (COUNT, MAX, MIN, AVG, SUM)

SELECT SUM(c.milage)
FROM car c
WHERE c.owner = 'Bill';

Execution Order FROM -> WHERE -> GROUP BY -> HAVING -> SELECT -> DISTINT -> ORDER BY

GROUP BY Clause

Break output set into subsets Run set function against each subset

SELECT COUNT(c.owner)
FROM car c
GROUP BY c.maker;

HAVING Clause

Works like WHERE clause to restrict result

SELECT DISTINT(c.owner)
FROM car c
HAVING SUM(c.milage) < 5000;

Joining Tables

The JOIN clause allow merges multiple tables into one result set

CROSS JOIN clause

Simplest JOIN, least useful All rows from both tables

SELECT c.maker, o.owner
FROM cars c, owner o;

INNER JOIN

OUTER JOIN

LEFT OUTER JOIN

RIGHT OUTER JOIN

SELF JOIN

UNION JOIN

Backing up your database

MySQL provides utilities, such as mysqldump, for database backup. They are good for small database backup. For medium to large databse, it is recommended to have physical backup.

Use mysqldump command for database backup. It will generate a script to recreate the databse and reinsert the data back one by one. Use mysql command to restore database.

mysqldump -h <hostname> -u <username> -p
or 
mysqldump --host=$SERVERNAME --user=$USERNAME --password=$PASSWORD

MySQL workbench or myphpadmin: GUI tool for manage and monitor MySQL database. It also allow you to import and export database

imhwli / mysqlnotes