09_MySQL数据库的索引机制

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);