MySQL - index

1、 brief introduction

MySQL The official definition of index is ： Indexes （Index） Help MySQL Data structure for efficient data acquisition .
Index in a small amount of data , Not very useful , But when it comes to big data , The difference is obvious .

2、 Classification of indexes

2.1、 primary key （PRIMARy KEY）

• The only sign , The primary key cannot be repeated , A table can only have one primary key .

2.2、 unique index （UNIQUE KEY）

• Avoid duplicate data , The unique index can be repeated , A table can have multiple unique indexes

2.3、 General index （KEY/INDEX）

• default ,index,key Keyword to set

2.4、 Full-text index （FullText）

• Only under the specific database engine ,MySAM
• Quickly locate data

3、 Test index

3.1、 establish 100 Ten thousand data

CREATE TABLE `app_user` (
`id` BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) DEFAULT'' COMMENT' The user nickname ',
`email` VARCHAR(50) NOT NULL COMMENT' User mailbox ',
`phone` VARCHAR(20) DEFAULT'' COMMENT' cell-phone number ',
`gender` TINYINT(4) UNSIGNED DEFAULT '0'COMMENT ' Gender （0： male ;1: Woman ）',
`password` VARCHAR(100) NOT NULL COMMENT ' password ',
`age` TINYINT(4) DEFAULT'0'  COMMENT ' Age ',
`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 COMMENT = 'app User table '

--  Insert 100 Play data 
DELIMITER $$ --  Before you write a function, you have to write , sign 
CREATE FUNCTION mock_data()
RETURNS INT
BEGIN
	DECLARE num INT DEFAULT 1000000;
	DECLARE i INT DEFAULT 0;
	WHILE i<num DO
		INSERT INTO app_user(`name`,`email`,`phone`,`gender`,`password`,`age`) 
		VALUES(CONCAT(' user ',i),'[email protected]',CONCAT('15',FLOOR(RAND()*(999999999-100000000)[phone])),
		FLOOR(RAND()*2),UUID(),FLOOR(RAND()*100));
		SET i=i+1;
	END WHILE;
	RETURN i;
END;
SELECT mock_data()

• Query the first 999999 Data ：SELECT * FROM app_user WHERE name=‘ user 999999’;
  

3.2、 Add index

-- id_ Table name _ Field name 
CREATE INDEX id_app_user_name ON app_user(`name`)

• Query the first 999999 Data ：SELECT * FROM app_user WHERE name=‘ user 999999’;
  

4、 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