wake_alone

计算a、b两个表中，值相等的某一列的数量group by … count()创建分组并且用聚集函数进行计算inner join—同时存在内联结—在两个表的交集中进行操作select a.id,COUNT(b.Id ) from a right outer join a ON a.** = b.** group by material.id;取得a，b两个表 相等的**列的值。每个值都同...

Mysql数据库常用操作Mysql建库、建表CREATE DATABASE spring_jdbc_test;DROP TABLE IF EXISTS `question_validate_log`;CREATE TABLE IF NOT EXISTS `student`( `id` int unsigned auto_increment, `name` VARCHAR(...

B/B+/B-树https://blog.youkuaiyun.com/sunshine_lyn/article/details/82747596https://www.cnblogs.com/liuqing576598117/p/11264243.htmlhttps://blog.youkuaiyun.com/qq_26222859/article/details/80631121聚簇索引和非聚簇索引http...