MySQL | 数据库的索引机制

数据排序的好处

• 一旦数据排序之后，查找的速度就会翻倍，现实世界跟程序世界都是如此

如何创建索引

	CREATE TABLE t_message(
	id INT UNSIGNED PRIMARY KEY,
	content VARCHAR(200) NOT NULL,
	type ENUM("公告", "通报", "个人通知") NOT NULL,
	create_time TIMESTAMP NOT NULL,
	INDEX idx_type (type)
	)

hosted with ❤ by GitHub

如何添加与删除索引

	DROP INDEX idx_type ON t_message;
	CREATE INDEX idx_type ON t_message(type);
	SHOW INDEX FROM t_message;
	ALTER TABLE t_message ADD INDEX idx_type(type);

hosted with ❤ by GitHub

索引的使用原则

• 数据库很大，而且经常被查询的数据表可以设置索引
• 索引只添加在经常被用作索引条件的字段上面
• 不要在大字段上创建索引

	CREATE TABLE t_message(
	id INT UNSIGNED PRIMARY KEY,
	content VARCHAR(200) NOT NULL,
	type ENUM("公告", "通报", "个人通知") NOT NULL,
	create_time TIMESTAMP NOT NULL,
	INDEX idx_type (type)
	);
	DROP INDEX idx_type ON t_message;
	CREATE INDEX idx_type ON t_message(type);
	SHOW INDEX FROM t_message;
	ALTER TABLE t_message ADD INDEX idx_type(type);

hosted with ❤ by GitHub