Mysql 高性能索引

1、减小索引长度取字段10个字符查看有多少数量select count(distinct left(device_token,10)) from t_client_info;取字段10个字符占总数百分比 查看区分度select count(distinct left(device_token,10)) /count(*) from t_client_info;取字段10个字符建立索引alter table t_client_info add index token (device_token(10));alter table t_device_token add index token (device_token(10)); alter table t_third_account add index open_id (open_id(10));alter table t_client_log add index token (token(10));设置字段默认插入当前时间alter table `t_app` add column `update_time` datetime NULL DEFAULT CURRENT_TIMESTAMP COMMENT '版本更新时间';