MySQL learning notes 2

MySQL function

Common functions

--  Mathematical operations 

SELECT ABS(-8) --  The absolute value 
SELECT CEILING(9.4) --  Rounding up 
SELECT FLOOR(9.4)  --  Rounding down 
SELECT RAND() --  return 0-1 random number 
SELECT SIGN(-10) --  Judge the sign of a number  0-0  A negative number returns -1  A positive number returns 1

--  String function 
SELECT CHAR_LENGTH('2323232') --  Return string length 
SELECT CONCAT(' I ','233') --  String concatenation 
SELECT INSERT('java',1,2,'cccc') --  Replace a length from a position 
SELECT UPPER('abc') 
SELECT LOWER('ABC')
SELECT REPLACE(' If you persist, you will succeed ',' insist ',' Strive ')

--  Check the last name   Zhou   Classmate  , Change to Zou 
SELECT REPLACE(studentname,' Zhou ',' Zou ') FROM student
WHERE studentname LIKE ' Zhou %'

--  Time and date functions （ remember ）
SELECT CURRENT_DATE() --  Get current date 
SELECT CURDATE() --  Get current date 
SELECT NOW() --  Get current date 
SELECT LOCATIME()  --  Local time 
SELECT SYSDATE()  --  system time 

SELECT YEAR(NOW())
SELECT MONTH(NOW())
SELECT DAY(NOW())
SELECT HOUR(NOW())
SELECT MINUTE(NOW())
SELECT SECOND(NOW())

--  System 
SELECT SYSTEM_USER()
SELECT USER()
SELECT VERSION()

Aggregate functions （ Commonly used ）

The name of the function	describe
COUNT()	Count
SUM()	Sum up
AVG()	Average
MAX()	Maximum
MIN()	minimum value
…

Database level MD5 encryption （ expand ）

What is? MD5

It mainly enhances the complexity and irreversibility of the algorithm .

MD5 Irreversible , Concrete MD5 It's the same

MD5 Principle of cracking , There is a dictionary behind it ,MD5 Encrypted value , Value before encryption

CREATE TABLE `testmd5`(
`id` INT(4) NOT NULL,
`name` VARCHAR(20) NOT NULL,
`pwd` VARCHAR(50) NOT NULL,
PRIMARY KEY (`id`)

)ENGINE=INNODB DEFAULT CHARSET=UTF8


--  Plaintext password 
INSERT INTO testmd5 VALUES(1,' Zhang San ','123456'),(2,' Li Si ','123456'),(3,' Wang Wu ','123456')

--  encryption 
UPDATE testmd5 SET pwd=MD5(pwd) WHERE id =1
UPDATE testmd5 SET pwd=MD5(pwd) WHERE id !=1  --  Encrypt all 

--  Encrypt on insert 

INSERT INTO testmd5 VALUES(4,' Xiao Ming ',MD5('123456'))
INSERT INTO testmd5 VALUES(5,' red ',MD5('123456'))

--  How to check , The password passed by the user , Conduct MD5 encryption , Then compare the encrypted values 
SELECT * FROM testmd5 WHERE `name`=' red ' AND pwd=MD5('123456')

Business

What is business

Business principles ： ACID principle Atomicity , Uniformity , Isolation, , persistence （ Dirty reading , Fantasy reading …）

Atomicity （Atomicity）

Either they all succeed , Or they all failed

Uniformity （Consistency）

The data integrity before and after the transaction should be consistent

Isolation, (Isolation)

When multiple concurrent transactions occur , Mutual interference

persistence （Durability）– Transaction submission

Once a transaction is committed, it is irreversible , Be persisted to the database

Perform transactions ：

-- mysql  Automatically turn on transaction commit 
SET autocommit=0 --  close 
SET autocommit=1 --  Turn on （ default ）

--  Handle transactions manually 
SET autocommit =0 --  Turn off auto submit 

--  The transaction open 

START TRANSACTION --  Mark the beginning of a transaction , After this SQP All in the same transaction 

INSERT XX
INSERT XX

--  Submit  ：  Persistence ( success )
COMMIT 
--  Roll back ：  Back to the original （ Failure ）
ROLLBACK
--  End of transaction 
SET autocommit = 1 --  Turn on auto submit 
--  understand 
SAVEPOINT  Save point name  --  Set a save point for a transaction 
ROLLBACK TO SAVEPOINT  Save roll call  --  Roll back to savepoint 
RELEASE SAVEPOINT  Save it  --  Delete savepoint 

Simulate transfer transactions ：

CREATE DATABASE shop CHARACTER SET utf8 COLLATE utf8_general_ci
USE shop
CREATE TABLE `account`(
`id` INT(3) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(30) NOT NULL,
`money` DECIMAL(9,2) NOT NULL,
PRIMARY KEY (`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8

INSERT INTO account(`name`,`money`)
VALUES('A',2000),('B',10000)

--  Analog transfer ： Business 
SET autocommit = 0; --  Turn off auto submit 
START TRANSACTION --  Open transaction （ A set of transactions ）
UPDATE account SET money = money-500 WHERE `name` = 'A' -- A  Transfer to B
UPDATE account SET money = money+500 WHERE `name` = 'B' -- B  Money received 

COMMIT ; --  Commit transaction 
ROLLBACK ; --  Roll back 

SET autocommit=1 --  Restore defaults 

Indexes

MySQL The establishment of index for MySQL It is very important to run efficiently , The index can be greatly improved MySQL Retrieval speed of .

Classification of indexes

In a table , The primary key index can only have one , There can be more than one unique index

primary key （PRIMARY KEY）
The only sign , The primary key cannot be repeated , There can only be one column as the primary key

unique index （UNIQUE KEY）
Avoid duplicate columns , The unique index can be repeated , Multiple columns can be identified as unique indexes

General index （KEY/INDEX）
default ,index,key Keyword to set

Full-text index （FULLTEXT）
Only under the characteristic database engine ,MyISAM
Quickly locate data

--  Use of index 
-- 1. Add indexes to fields when creating tables 
-- 2. After creation , Add index 

--  Show all index information 
SHOW INDEX FROM  surface 

--  Add an index 
ALTER TABLE  surface  ADD FULLTEXT INDEX  Index name （ Field name ）

-- EXPLAIN  analysis sql Implementation status 
EXPLAIN SELECT * FROM student --  Non full text index 
EXPLAIN SELECT * FROM student WHERE MATCH(studentName) AGAINST(' Liu ')

Test index

add to 100 Ten thousand data test indexes improve the query speed

CREATE TABLE `app_user` (
`id` BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) DEFAULT '',
`email` VARCHAR(50) NOT NULL,
`phone` VARCHAR(20) DEFAULT '',
`gender` TINYINT(4) UNSIGNED DEFAULT '0',
`password` VARCHAR(100) NOT NULL DEFAULT '',
`age` TINYINT(4) DEFAULT NULL,
`create_time` DATETIME DEFAULT CURRENT_TIMESTAMP,
`update_time` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8

--  Insert 100 All the data 
DELIMITER $$ --  Before you write a function, you must write 
CREATE FUNCTION mock_data()
RETURNS INT 
BEGIN
DECLARE num INT DEFAULT 1000000;
DECLARE i INT DEFAULT 0;

WHILE i<num DO
--  Insert statement 
INSERT INTO app_user(`name`,`email`,`phone`,`gender`,`password`,`age`)
VALUE(CONCAT(' user ',i),'[email protected]',FLOOR (CONCAT('18',RAND()*9999999)),FLOOR (RAND()*2),
UUID(),FLOOR (RAND()*100));

SET i = i+1;
END WHILE;
RETURN i;


END;

INSERT INTO app_user(`name`,`email`,`phone`,`gender`,`password`,`age`)
VALUE(CONCAT(' user ',i),'[email protected]',FLOOR (CONCAT('18',RAND()*9999999)),FLOOR (RAND()*2),
UUID(),FLOOR (RAND()*100))


SELECT mock_data();

SELECT * FROM app_user WHERE `name`=' user 9999' --  Nearly half a second 

EXPLAIN SELECT * FROM app_user WHERE `name`=' user 9999'  --  Inquire about 99999 Bar record 

-- id _  Table name _ Field name 
-- create index on  Field 
CREATE INDEX id_app_user_name ON app_user(`name`); -- 0.001 s
EXPLAIN SELECT * FROM app_user WHERE `name`=' user 9999'  --  Look up a record 

When indexing small data , Not very useful , But when it comes to big data , The difference is obvious

Indexing principles

• More indexes is not better
• Don't index frequently changing data
• A table with a small amount of data does not need to be indexed
• The index is usually added to the fields commonly used for query

The data structure of the index

Hash Index of type

Btree: Default innodb Data structure of

read ： http://blog.codinglabs.org/articles/theory-of-mysql-index.html

Rights management and backup

User management

SQLyog Visual management

SQL The command operation
User table ：mysql.user

The essence ： Check this table , Additions and deletions

--  Create user  CREATE USER  user name  IDENTIFIED BY ' password '
CREATE USER sanjin IDENTIFIED BY '123456'

--  Change Password （ Change the current password ）
SET PASSWORD = PASSWORD('111111')


--  Change Password （ Change the specified user password ）

SET PASSWORD FOR sanjin = PASSWORD('111111')


--  rename  rename user  Original name  to  New name 
RENAME USER sanjin TO sanjin2

--  User authorization  ALL PRIVILEGES  All permissions   library , surface 
-- ALL PRIVILEGES  In addition to empowering others , Everything else can 
GRANT ALL PRIVILEGES ON *.* TO sanjin2

--  Query authority 
SHOW GRANTS FOR sanjin2  --  View the permissions for the specified user 
SHOW GRANTS FOR root@localhost


--  Revoke authority  REVOKE  What authority , In which library , To whom 
REVOKE ALL PRIVILEGES ON *.* FROM sanjin2

--  Delete user 
DROP USER sanjin2

MySQL Backup

Why backup ：

• Ensure that important data is not lost
• Data transfer

MySQL The way of database backup

• Copy physical files directly
• stay SQLyog Manually export... In this visualization tool
• In the table or library you want to export , Right click to select backup and Export

Standardize database design

When the database is complex , We need to design

Bad database design ：

• data redundancy , Waste space
• Database insertion and deletion are troublesome , abnormal 【 Shielding uses physical foreign keys 】
• The performance of the program is poor

Good database design ：

• Save memory space
• Ensure the integrity of the database
• It's convenient for us to develop the system

Software development , About the design of database

• Analyze requirements ： Analyze the business and the database needs to be processed
• Outline design ： Design diagrams E-R chart

The steps to design a database （ Take personal blog as an example ）

To collect information , Analyze requirements

• User table （ User login and logout , User's personal information , Blogging , Create classification ）
• Classification table （ The article classification , Who created ）
• Article table （ Information about the article ）
• Friend list （ Friend chain information ）
• Custom table （ system information , A key word , Or some main fields ）
• Tell me about the watch （ Publish your mood …id ,content ,time）

Identifying entities （ Implement the requirements to each field ）

Identify the relationship between entities

• Blogging user–>blog
• Create classification user–>category
• Focus on user–>user
• Friend chain –>links
• Comment on user–>user

Three paradigms

Why data normalization is needed ？

• Repetition of information
• Update exception
• Insertion exception
• Delete exception
  The exception cannot be displayed normally
  Loss of valid information

Three paradigms
First normal form （1NF）

• Atomicity ： Make sure that each column is no longer divisible

Second normal form （2NF）

• Premise ： Satisfy the first paradigm
• Each table only describes one thing

Third normal form （3NF）

• Premise ： Satisfy the first paradigm and the second paradigm
• The third paradigm needs to ensure that each column of data in the data table is directly related to the primary key , Not indirectly .

Normative and performance issues

• Table associated with query , No more than three tables
• Consider the needs and goals of commercialization （ Cost and user experience ） Database performance is more important
• When re standardizing performance problems , It needs proper consideration , Normative
• Deliberately add some redundant fields to some tables （ From multiple tables , Turn it into a single table ）
• Intentionally add some calculation Columns （ Reduce the amount of data from large to small ： Indexes ）