weixin_42904196的博客

mysql is null is not null != 对索引的影响基于mysql5.7 mac下测试创建表CREATE TABLE IF NOT EXISTS test (id INT ( 10 ) PRIMARY KEY auto_increment, name varchar( 255 ), status INT ( 10 ) UNSIGNED NOT NULL);第一种情况 name 字段建立索引 可以为空CREATE INDEX in_name ON test (name);